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98-408: The simplest labels are V+ and V− , but internal design and historical traditions have led to a variety of other labels being used. V+ and V− may also refer to the non-inverting (+) and inverting (−) voltage inputs of ICs like op amps . For power supplies, sometimes one of the supply rails is referred to as ground (abbreviated "GND") – positive and negative voltages are relative to

196-419: A Darlington pair ). This current signal develops a voltage at the bases of output transistors Q14 and Q20 proportional to the h ie of the respective transistor. Output transistors Q14 and Q20 are each configured as an emitter follower, so no voltage gain occurs there; instead, this stage provides current gain, equal to the h fe of Q14 and Q20. The current gain lowers the output impedance and although

294-491: A capacitor to store the analog voltage at the input, and using an electronic switch or gate to disconnect the capacitor from the input. Many ADC integrated circuits include the sample and hold subsystem internally. An ADC works by sampling the value of the input at discrete intervals in time. Provided that the input is sampled above the Nyquist rate , defined as twice the highest frequency of interest, then all frequencies in

392-437: A digital encoder logic circuit that generates a binary number on the output lines for each voltage range. ADCs of this type have a large die size and high power dissipation. They are often used for video , wideband communications , or other fast signals in optical and magnetic storage . The circuit consists of a resistive divider network, a set of op-amp comparators and a priority encoder. A small amount of hysteresis

490-438: A saw-tooth signal that ramps up or down then quickly returns to zero. When the ramp starts, a timer starts counting. When the ramp voltage matches the input, a comparator fires, and the timer's value is recorded. Timed ramp converters can be implemented economically, however, the ramp time may be sensitive to temperature because the circuit generating the ramp is often a simple analog integrator . A more accurate converter uses

588-470: A 500 Hz sine wave. To avoid aliasing, the input to an ADC must be low-pass filtered to remove frequencies above half the sampling rate. This filter is called an anti-aliasing filter , and is essential for a practical ADC system that is applied to analog signals with higher frequency content. In applications where protection against aliasing is essential, oversampling may be used to greatly reduce or even eliminate it. Although aliasing in most systems

686-428: A GBWP of hundreds of megahertz. For very high-frequency circuits, a current-feedback operational amplifier is often used. Modern integrated FET or MOSFET op amps approximate more closely the ideal op amp than bipolar ICs when it comes to input impedance and input bias currents. Bipolars are generally better when it comes to input voltage offset, and often have lower noise. Generally, at room temperature, with

784-526: A bigger picture, where, to continue with bipolar-transistor examples, although the FET remains entirely analogous, DC or bias currents into or out of each terminal may be written I C , I E , and I B . Apart from DC or bias conditions, many transistor circuits also process a smaller audio-, video-, or radio-frequency signal that is superimposed on the bias at the terminals. Lower-case letters and subscripts are used to refer to these signal levels at

882-459: A cascaded differential amplifier (outlined in dark blue) followed by a current-mirror active load . This constitutes a transconductance amplifier , turning a differential voltage signal at the bases of Q1, Q2 into a current signal into the base of Q15. It entails two cascaded transistor pairs, satisfying conflicting requirements. The first stage consists of the matched NPN emitter follower pair Q1, Q2 that provide high input impedance. The second

980-491: A clocked counter driving a DAC. A special advantage of the ramp-compare system is that converting a second signal just requires another comparator and another register to store the timer value. To reduce sensitivity to input changes during conversion, a sample and hold can charge a capacitor with the instantaneous input voltage and the converter can time the time required to discharge with a constant current . An integrating ADC (also dual-slope or multi-slope ADC) applies

1078-525: A constant current source . The time required to discharge the capacitor is proportional to the amplitude of the input voltage. While the capacitor is discharging, pulses from a high-frequency oscillator clock are counted by a register. The number of clock pulses recorded in the register is also proportional to the input voltage. If the analog value to measure is represented by a resistance or capacitance, then by including that element in an RC circuit (with other resistances or capacitances fixed) and measuring

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1176-498: A decrease in base drive for Q15. On the other hand, a small positive change in voltage at the non-inverting input (Q1 base) drives this transistor into conduction, reflected in an increase in current at the collector of Q3. This current drives Q7 further into conduction, which turns on current mirror Q5/Q6. Thus, the increase in Q3 emitter current is mirrored in an increase in Q6 collector current;

1274-399: A fairly large signal, and limited bandwidth, FET and MOSFET op amps now offer better performance. Sourced by many manufacturers, and in multiple similar products, an example of a bipolar transistor operational amplifier is the 741 integrated circuit designed in 1968 by David Fullagar at Fairchild Semiconductor after Bob Widlar 's LM301 integrated circuit design. In this discussion, we use

1372-432: A faithful reproduction of the original signal is only possible if the sampling rate is higher than twice the highest frequency of the signal. Since a practical ADC cannot make an instantaneous conversion, the input value must necessarily be held constant during the time that the converter performs a conversion (called the conversion time ). An input circuit called a sample and hold performs this task—in most cases by using

1470-446: A flow of digital values. It is therefore required to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter. A continuously varying bandlimited signal can be sampled and then the original signal can be reproduced from the discrete-time values by a reconstruction filter . The Nyquist–Shannon sampling theorem implies that

1568-411: A given voltage, using them to conserve energy by switching off supplies to components that are not in active use. More advanced circuits often have pins carrying voltage levels for more specialized functions, and these are generally labeled with some abbreviation of their purpose. For example, V USB for the supply delivered to a USB device (nominally 5 V), V BAT for a battery, or V ref for

1666-422: A known voltage charging and discharging curve that can be used to solve for an unknown analog value. The Wilkinson ADC was designed by Denys Wilkinson in 1950. The Wilkinson ADC is based on the comparison of an input voltage with that produced by a charging capacitor. The capacitor is allowed to charge until a comparator determines it matches the input voltage. Then, the capacitor is discharged linearly by using

1764-436: A longer time to measure than smaller one. And the accuracy is limited by the accuracy of the microcontroller clock and the amount of time available to measure the value, which potentially might even change during measurement or be affected by external parasitics . A direct-conversion or flash ADC has a bank of comparators sampling the input signal in parallel, each firing for a specific voltage range. The comparator bank feeds

1862-483: A much larger voltage signal on output. The input stage with Q1 and Q3 is similar to an emitter-coupled pair (long-tailed pair), with Q2 and Q4 adding some degenerating impedance. The input impedance is relatively high because of the small current through Q1-Q4. A typical 741 op amp has a differential input impedance of about 2 MΩ. The common mode input impedance is even higher, as the input stage works at an essentially constant current. A differential voltage V in at

1960-409: A pulse of a particular amplitude is always converted to the same digital value. The problem lies in that the ranges of analog values for the digitized values are not all of the same widths, and the differential linearity decreases proportionally with the divergence from the average width. The sliding scale principle uses an averaging effect to overcome this phenomenon. A random, but known analog voltage

2058-402: A resistive feedback network). The amplifier's differential inputs consist of a non-inverting input (+) with voltage V + and an inverting input (−) with voltage V − ; ideally the op amp amplifies only the difference in voltage between the two, which is called the differential input voltage . The output voltage of the op amp V out is given by the equation where A OL

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2156-454: A sampler. It cannot improve the linearity, and thus accuracy does not necessarily improve. Quantization distortion in an audio signal of very low level with respect to the bit depth of the ADC is correlated with the signal and sounds distorted and unpleasant. With dithering, the distortion is transformed into noise. The undistorted signal may be recovered accurately by averaging over time. Dithering

2254-519: A sampling rate greater than twice the bandwidth of the signal, then per the Nyquist–Shannon sampling theorem , near-perfect reconstruction is possible. The presence of quantization error limits the SNDR of even an ideal ADC. However, if the SNDR of the ADC exceeds that of the input signal, then the effects of quantization error may be neglected, resulting in an essentially perfect digital representation of

2352-473: A small-signal differential current in Q3 versus Q4 appears summed (doubled) at the base of Q15, the input of the voltage gain stage. The (class-A) voltage gain stage (outlined in magenta ) consists of the two NPN transistors Q15 and Q19 connected in a Darlington configuration and uses the output side of current mirror formed by Q12 and Q13 as its collector (dynamic) load to achieve its high voltage gain. The output sink transistor Q20 receives its base drive from

2450-661: Is V BE  / 50 kΩ, about 35 μA, as is the quiescent current in Q15, with its matching operating point. Thus, the quiescent currents are pairwise matched in Q1/Q2, Q3/Q4, Q5/Q6, and Q7/Q15. Quiescent currents in Q16 and Q19 are set by the current mirror Q12/Q13, which is running at ~1 mA. The collector current in Q19 tracks that standing current. In the circuit involving Q16 (variously named rubber diode or V BE multiplier),

2548-524: Is a DC-coupled electronic voltage amplifier with a differential input , a (usually) single-ended output, and an extremely high gain . Its name comes from its original use of performing mathematical operations in analog computers . By using negative feedback , an op amp circuit 's characteristics (e.g. its gain, input and output impedance , bandwidth , and functionality) can be determined by external components and have little dependence on temperature coefficients or engineering tolerance in

2646-430: Is a system that converts an analog signal , such as a sound picked up by a microphone or light entering a digital camera , into a digital signal . An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that

2744-454: Is a very small amount of random noise (e.g. white noise ), which is added to the input before conversion. Its effect is to randomize the state of the LSB based on the signal. Rather than the signal simply getting cut off altogether at low levels, it extends the effective range of signals that the ADC can convert, at the expense of a slight increase in noise. Dither can only increase the resolution of

2842-535: Is added to the sampled input voltage. It is then converted to digital form, and the equivalent digital amount is subtracted, thus restoring it to its original value. The advantage is that the conversion has taken place at a random point. The statistical distribution of the final levels is decided by a weighted average over a region of the range of the ADC. This in turn desensitizes it to the width of any specific level. These are several common ways of implementing an electronic ADC. Resistor-capacitor (RC) circuits have

2940-471: Is also used in integrating systems such as electricity meters . Since the values are added together, the dithering produces results that are more exact than the LSB of the analog-to-digital converter. Dither is often applied when quantizing photographic images to a fewer number of bits per pixel—the image becomes noisier but to the eye looks far more realistic than the quantized image, which otherwise becomes banded . This analogous process may help to visualize

3038-428: Is built into the comparator to resolve any problems at voltage boundaries. At each node of the resistive divider, a comparison voltage is available. The purpose of the circuit is to compare the analog input voltage with each of the node voltages. The circuit has the advantage of high speed as the conversion takes place simultaneously rather than sequentially. Typical conversion time is 100 ns or less. Conversion time

IC power-supply pin - Misplaced Pages Continue

3136-586: Is derived by contraction. In this convention, v i and v o usually refer to the external input and output voltages of the circuit or stage. Similar conventions were applied to circuits involving vacuum tubes , or thermionic valves , as they were known outside of the U.S. Therefore, we see V P , V K , and V G referring to plate (or anode outside of the U.S.), cathode (note K , not C ) and grid voltages in analyses of vacuum triode , tetrode , and pentode circuits. Op amp An operational amplifier (often op amp or opamp )

3234-485: Is determined primarily by the feedback network, rather than by the op-amp characteristics. If the feedback network is made of components with values small relative to the op amp's input impedance, the value of the op amp's open-loop response A OL does not seriously affect the circuit's performance. In this context, high input impedance at the input terminals and low output impedance at the output terminal(s) are particularly useful features of an op amp. The response of

3332-427: Is limited only by the speed of the comparator and of the priority encoder. This type of ADC has the disadvantage that the number of comparators required almost doubles for each added bit. Also, the larger the value of n, the more complex is the priority encoder. A successive-approximation ADC uses a comparator and a binary search to successively narrow a range that contains the input voltage. At each successive step,

3430-489: Is limited relevance of these device-specific power-supply designations in circuits that use a mixture of bipolar and FET elements, or in those that employ either both NPN and PNP transistors or both n - and p -channel FETs. This latter case is very common in modern chips, which are often based on CMOS technology, where the C stands for complementary , meaning that complementary pairs of n - and p -channel devices are common throughout. These naming conventions were part of

3528-513: Is mirrored from Q8 into Q9, where it is summed with the collector current in Q10, the result being applied to the bases of Q3 and Q4. The quiescent currents through Q1 and Q3 (also Q2 and Q4) i 1 will thus be half of i 10 , of order ~10 μA. Input bias current for the base of Q1 (also Q2) will amount to i 1  / β; typically ~50 nA, implying a current gain h fe  ≈ 200 for Q1 (also Q2). This feedback circuit tends to draw

3626-424: Is not well controlled by the manufacturing process, and so it is impractical to use an open-loop amplifier as a stand-alone differential amplifier . Without negative feedback , and optionally positive feedback for regeneration , an open-loop op amp acts as a comparator , although comparator ICs are better suited. If the inverting input is held at ground (0 V), and the input voltage V in applied to

3724-411: Is one type of differential amplifier . Other differential amplifier types include the fully differential amplifier (an op amp with a differential rather than single-ended output), the instrumentation amplifier (usually built from three op amps), the isolation amplifier (with galvanic isolation between input and output), and negative-feedback amplifier (usually built from one or more op amps and

3822-467: Is proportional to the input, but there are other possibilities. There are several ADC architectures . Due to the complexity and the need for precisely matched components , all but the most specialized ADCs are implemented as integrated circuits (ICs). These typically take the form of metal–oxide–semiconductor (MOS) mixed-signal integrated circuit chips that integrate both analog and digital circuits . A digital-to-analog converter (DAC) performs

3920-441: Is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of an external feedback loop from the output to the input). The magnitude of A OL is typically very large (100,000 or more for integrated circuit op amps, corresponding to +100  dB ). Thus, even small microvolts of difference between V + and V − may drive the amplifier into clipping or saturation . The magnitude of A OL

4018-459: Is the ADC's resolution in bits and E FSR is the full-scale voltage range (also called 'span'). E FSR is given by where V RefHi and V RefLow are the upper and lower extremes, respectively, of the voltages that can be coded. Normally, the number of voltage intervals is given by where M is the ADC's resolution in bits. That is, one voltage interval is assigned in between two consecutive code levels. Example: In many cases,

IC power-supply pin - Misplaced Pages Continue

4116-405: Is the matched PNP common-base pair Q3, Q4 that eliminates the undesirable Miller effect ; it drives an active load Q7 plus matched pair Q5, Q6. That active load is implemented as a modified Wilson current mirror ; its role is to convert the (differential) input current signal to a single-ended signal without the attendant 50% losses (increasing the op amp's open-loop gain by 3 dB). Thus,

4214-414: Is the number of ADC bits. Clock jitter is caused by phase noise . The resolution of ADCs with a digitization bandwidth between 1 MHz and 1 GHz is limited by jitter. For lower bandwidth conversions such as when sampling audio signals at 44.1 kHz, clock jitter has a less significant impact on performance. An analog signal is continuous in time and it is necessary to convert this to

4312-407: Is uniformly distributed between − 1 ⁄ 2 LSB and + 1 ⁄ 2 LSB, and the signal has a uniform distribution covering all quantization levels, the signal-to-quantization-noise ratio (SQNR) is given by where Q is the number of quantization bits. For example, for a 16-bit ADC, the quantization error is 96.3 dB below the maximum level. Quantization error is distributed from DC to

4410-404: Is unwanted, it can be exploited to provide simultaneous down-mixing of a band-limited high-frequency signal (see undersampling and frequency mixer ). The alias is effectively the lower heterodyne of the signal frequency and sampling frequency. For economy, signals are often sampled at the minimum rate required with the result that the quantization error introduced is white noise spread over

4508-479: The Nyquist frequency . Consequently, if part of the ADC's bandwidth is not used, as is the case with oversampling , some of the quantization error will occur out-of-band , effectively improving the SQNR for the bandwidth in use. In an oversampled system, noise shaping can be used to further increase SQNR by forcing more quantization error out of band. In ADCs, performance can usually be improved using dither . This

4606-470: The bandlimited analog input signal. The resolution of the converter indicates the number of different, i.e. discrete, values it can produce over the allowed range of analog input values. Thus a particular resolution determines the magnitude of the quantization error and therefore determines the maximum possible signal-to-noise ratio for an ideal ADC without the use of oversampling . The input samples are usually stored electronically in binary form within

4704-463: The effective number of bits (ENOB) below that predicted by quantization error alone. The error is zero for DC, small at low frequencies, but significant with signals of high amplitude and high frequency. The effect of jitter on performance can be compared to quantization error: Δ t < 1 2 q π f 0 {\displaystyle \Delta t<{\frac {1}{2^{q}\pi f_{0}}}} , where q

4802-553: The more common circuit configurations . In equivalence to the difference between NPN and PNP bipolars, V DD is positive with regard to V SS in the case of n -channel FETs and MOSFETs and negative for circuits based on p -channel FETs and MOSFETs. CMOS ICs have generally borrowed the NMOS convention of V DD for positive and V SS for negative, even though both positive and negative supply rails connect to source terminals (the positive supply goes to PMOS sources,

4900-408: The signal-to-noise ratio performance of the ADC and thus reduce its effective resolution. When digitizing a sine wave x ( t ) = A sin ⁡ ( 2 π f 0 t ) {\displaystyle x(t)=A\sin {(2\pi f_{0}t)}} , the use of a non-ideal sampling clock will result in some uncertainty in when samples are recorded. Provided that

4998-435: The voltage divider R f , R g determines the closed-loop gain A CL  = V out / V in . Equilibrium will be established when V out is just sufficient to pull the inverting input to the same voltage as V in . The voltage gain of the entire circuit is thus 1 + R f / R g . As a simple example, if V in  = 1 V and R f  = R g , V out will be 2 V, exactly

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5096-514: The 4.5 kΩ resistor must be conducting about 100 μA, with Q16 V BE roughly 700 mV. Then V CB must be about 0.45 V and V CE at about 1.0 V. Because the Q16 collector is driven by a current source and the Q16 emitter drives into the Q19 collector current sink, the Q16 transistor establishes a voltage difference between the Q14 base and the Q20 base of ~1 V, regardless of

5194-421: The ADC, so the resolution is usually expressed as the audio bit depth . In consequence, the number of discrete values available is usually a power of two. For example, an ADC with a resolution of 8 bits can encode an analog input to one in 256 different levels (2  = 256). The values can represent the ranges from 0 to 255 (i.e. as unsigned integers) or from −128 to 127 (i.e. as signed integer), depending on

5292-804: The DC voltages, the furthest voltage, beyond these resistors or other components if present, was often referred to as V CC , V EE , and V BB . In practice V CC and V EE then refer to the positive and negative supply lines respectively in common NPN circuits. Note that V CC would be negative, and V EE would be positive in equivalent PNP circuits. The V BB specifies reference bias supply voltage in ECL logic. Exactly analogous conventions were applied to field-effect transistors with their drain, source and gate terminals. This led to V D and V S being created by supply voltages designated V DD and V SS in

5390-519: The actual sampling time uncertainty due to clock jitter is Δ t {\displaystyle \Delta t} , the error caused by this phenomenon can be estimated as E a p ≤ | x ′ ( t ) Δ t | ≤ 2 A π f 0 Δ t {\displaystyle E_{ap}\leq |x'(t)\Delta t|\leq 2A\pi f_{0}\Delta t} . This will result in additional recorded noise that will reduce

5488-597: The amount required to keep V − at 1 V. Because of the feedback provided by the R f , R g network, this is a closed-loop circuit. Another way to analyze this circuit proceeds by making the following (usually valid) assumptions: The input signal V in appears at both (+) and (−) pins per assumption 1, resulting in a current i through R g equal to V in / R g : i = V in R g {\displaystyle i={\frac {V_{\text{in}}}{R_{\text{g}}}}} Since Kirchhoff's current law states that

5586-409: The application. Resolution can also be defined electrically, and expressed in volts . The change in voltage required to guarantee a change in the output code level is called the least significant bit (LSB) voltage. The resolution Q of the ADC is equal to the LSB voltage. The voltage resolution of an ADC is equal to its overall voltage measurement range divided by the number of intervals: where M

5684-518: The base of Q15 (the input of the voltage gain stage) is V in g m  / 2. This portion of the op amp cleverly changes a differential signal at the op amp inputs to a single-ended signal at the base of Q15, and in a way that avoids wastefully discarding the signal in either leg. To see how, notice that a small negative change in voltage at the inverting input (Q2 base) drives it out of conduction, and this incremental decrease in current passes directly from Q4 collector to its emitter, resulting in

5782-410: The closed-loop gain A CL : A CL = V out V in = 1 + R f R g {\displaystyle A_{\text{CL}}={\frac {V_{\text{out}}}{V_{\text{in}}}}=1+{\frac {R_{\text{f}}}{R_{\text{g}}}}} An ideal op amp is usually considered to have the following characteristics: These ideals can be summarized by

5880-547: The common base node of Q3/Q4 to a voltage V com  − 2  V BE , where V com is the input common-mode voltage. At the same time, the magnitude of the quiescent current is relatively insensitive to the characteristics of the components Q1–Q4, such as h fe , that would otherwise cause temperature dependence or part-to-part variations. Transistor Q7 drives Q5 and Q6 into conduction until their (equal) collector currents match that of Q1/Q3 and Q2/Q4. The quiescent current in Q7

5978-443: The common collectors of Q15 and Q19; the level-shifter Q16 provides base drive for the output source transistor Q14. The transistor Q22 prevents this stage from delivering excessive current to Q20 and thus limits the output sink current. The output stage (Q14, Q20, outlined in cyan) is a Class AB amplifier. It provides an output drive with impedance of ~50   Ω, in essence, current gain. Transistor Q16 (outlined in green) provides

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6076-540: The common-mode voltage of Q14/Q20 bases. The standing current in Q14/Q20 will be a factor exp(100 mV mm/ V T ) ≈ 36 smaller than the 1 mA quiescent current in the class A portion of the op amp. This (small) standing current in the output transistors establishes the output stage in class AB operation and reduces the crossover distortion of this stage. A small differential input voltage signal gives rise, through multiple stages of current amplification, to

6174-419: The conversion periodically, sampling the input, and limiting the allowable bandwidth of the input signal. The performance of an ADC is primarily characterized by its bandwidth and signal-to-noise and distortion ratio (SNDR). The bandwidth of an ADC is characterized primarily by its sampling rate . The SNDR of an ADC is influenced by many factors, including the resolution , linearity and accuracy (how well

6272-415: The converter compares the input voltage to the output of an internal digital-to-analog converter (DAC) which initially represents the midpoint of the allowed input voltage range. At each step in this process, the approximation is stored in a successive approximation register (SAR) and the output of the digital-to-analog converter is updated for a comparison over a narrower range. A ramp-compare ADC produces

6370-413: The double-letter supply voltage subscript notation is not directly linked (though it may have been an influencing factor). ICs using bipolar junction transistors have V CC (+, positive) and V EE (-, negative) power-supply pins – though V CC is also often used for CMOS devices as well. In circuit diagrams and circuit analysis, there are long-standing conventions regarding

6468-417: The effect of dither on an analog audio signal that is converted to digital. An ADC has several sources of errors. Quantization error and (assuming the ADC is intended to be linear) non- linearity are intrinsic to any analog-to-digital conversion. These errors are measured in a unit called the least significant bit (LSB). In the above example of an eight-bit ADC, an error of one LSB is 1 ⁄ 256 of

6566-423: The emitter resistor of Q10, and 28 mV is V T , the thermal voltage at room temperature. In this case i 10  ≈ 20 μA. The biasing circuit of this stage is set by a feedback loop that forces the collector currents of Q10 and Q9 to (nearly) match. Any small difference in these currents provides drive for the common base of Q3 and Q4. The summed quiescent currents through Q1 and Q3 plus Q2 and Q4

6664-499: The full signal range, or about 0.4%. All ADCs suffer from nonlinearity errors caused by their physical imperfections, causing their output to deviate from a linear function (or some other function, in the case of a deliberately nonlinear ADC) of their input. These errors can sometimes be mitigated by calibration , or prevented by testing. Important parameters for linearity are integral nonlinearity and differential nonlinearity . These nonlinearities introduce distortion that can reduce

6762-436: The ground. In digital electronics, negative voltages are seldom present, and the ground nearly always is the lowest voltage level. In analog electronics (e.g. an audio power amplifier ) the ground can be a voltage level between the most positive and most negative voltage level. While double subscript notation , where subscripted letters denote the difference between two points, uses similar-looking placeholders with subscripts,

6860-415: The increased collector currents shunts more from the collector node and results in a decrease in base drive current for Q15. Besides avoiding wasting 3 dB of gain here, this technique decreases common-mode gain and feedthrough of power supply noise. A current signal i at Q15's base gives rise to a current in Q19 of order i β (the product of the h fe of each of Q15 and Q19, which are connected in

6958-494: The logarithm of the resolution, i.e. the number of bits. Flash ADCs are certainly the fastest type of the three; The conversion is basically performed in a single parallel step. There is a potential tradeoff between speed and precision. Flash ADCs have drifts and uncertainties associated with the comparator levels results in poor linearity. To a lesser extent, poor linearity can also be an issue for successive-approximation ADCs. Here, nonlinearity arises from accumulating errors from

7056-482: The naming of voltages, currents, and some components. In the analysis of a bipolar junction transistor, for example, in a common-emitter configuration, the DC voltage at the collector, emitter, and base (with respect to ground) may be written as V C , V E , and V B respectively. Resistors associated with these transistor terminals may be designated R C , R E , and R B . In order to create

7154-477: The negative supply to NMOS sources). In many single-supply digital and analog circuits the negative power supply is also called "GND". In "split-rail" supply systems there are multiple supply voltages. Examples of such systems include modern cell phones, with GND and voltages such as 1.2 V, 1.8 V, 2.4 V, 3.3 V, and PCs, with GND and voltages such as −5 V, 3.3 V, 5 V, 12 V. Power-sensitive designs often have multiple power rails at

7252-411: The non-inverting input is positive, the output will be maximum positive; if V in is negative, the output will be maximum negative. If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to the inverting input. The closed-loop feedback greatly reduces the gain of the circuit. When negative feedback is used, the circuit's overall gain and response

7350-408: The op amp inputs (pins 3 and 2, respectively) gives rise to a small differential current in the bases of Q1 and Q2 i in  ≈ V in  / (2 h ie h fe ). This differential base current causes a change in the differential collector current in each leg by i in h fe . Introducing the transconductance of Q1, g m  = h fe  / h ie , the (small-signal) current at

7448-489: The op amp itself. This flexibility has made the op amp a popular building block in analog circuits . Today, op amps are used widely in consumer, industrial, and scientific electronics. Many standard integrated circuit op amps cost only a few cents; however, some integrated or hybrid operational amplifiers with special performance specifications may cost over US$ 100. Op amps may be packaged as components or used as elements of more complex integrated circuits . The op amp

7546-429: The op-amp circuit with its input, output, and feedback circuits to an input is characterized mathematically by a transfer function ; designing an op-amp circuit to have a desired transfer function is in the realm of electrical engineering . The transfer functions are important in most applications of op amps, such as in analog computers . In the non-inverting amplifier on the right, the presence of negative feedback via

7644-453: The op-amp model. The designer can then include these effects into the overall performance of the final circuit. Some parameters may turn out to have negligible effect on the final design while others represent actual limitations of the final performance. Real op amps differ from the ideal model in various aspects. Typical low-cost, general-purpose op amps exhibit a GBWP of a few megahertz. Specialty and high-speed op amps exist that can achieve

7742-584: The output impedance is not zero, as it would be in an ideal op amp, with negative feedback it approaches zero at low frequencies. The net open-loop small-signal voltage gain of the op amp is determined by the product of the current gain h fe of some 4 transistors. In practice, the voltage gain for a typical 741-style op amp is of order 200,000, and the current gain, the ratio of input impedance (~2−6   MΩ) to output impedance (~50   Ω) provides yet more (power) gain. The ideal op amp has infinite common-mode rejection ratio , or zero common-mode gain. In

7840-504: The parameters of the hybrid-pi model to characterize the small-signal, grounded emitter characteristics of a transistor. In this model, the current gain of a transistor is denoted h fe , more commonly called the β. A small-scale integrated circuit , the 741 op amp shares with most op amps an internal structure consisting of three gain stages: Additionally, it contains current mirror (outlined red) bias circuitry and compensation capacitor (30 pF). The input stage consists of

7938-410: The performance of the ADC can be greatly increased at little or no cost. Furthermore, as any aliased signals are also typically out of band, aliasing can often be eliminated using very low cost filters. The speed of an ADC varies by type. The Wilkinson ADC is limited by the clock rate which is processable by current digital circuits. For a successive-approximation ADC , the conversion time scales with

8036-533: The present circuit, if the input voltages change in the same direction, the negative feedback makes Q3/Q4 base voltage follow (with 2 V BE below) the input voltage variations. Now the output part (Q10) of Q10-Q11 current mirror keeps up the common current through Q9/Q8 constant in spite of varying voltage. Q3/Q4 collector currents, and accordingly the output current at the base of Q15, remain unchanged. Analog-to-digital converter In electronics , an analog-to-digital converter ( ADC , A/D , or A-to-D )

8134-411: The quantization levels match the true analog signal), aliasing and jitter . The SNDR of an ADC is often summarized in terms of its effective number of bits (ENOB), the number of bits of each measure it returns that are on average not noise . An ideal ADC has an ENOB equal to its resolution. ADCs are chosen to match the bandwidth and required SNDR of the signal to be digitized. If an ADC operates at

8232-500: The quiescent current for the output transistors and Q17 limits output source current. Biasing circuits provide appropriate quiescent current for each stage of the op amp. The resistor (39 kΩ) connecting the (diode-connected) Q11 and Q12, and the given supply voltage ( V S +  −  V S − ), determine the current in the current mirrors , (matched pairs) Q10/Q11 and Q12/Q13. The collector current of Q11, i 11 × 39 kΩ = V S + − V S − − 2  V BE . For

8330-489: The reference voltage for an analog-to-digital converter . Systems combining both digital and analog circuits often distinguish digital and analog grounds (GND and AGND), helping isolate digital noise from sensitive analog circuits. High-security cryptographic devices and other secure systems sometimes require separate power supplies for their unencrypted and encrypted ( red/black ) subsystems to prevent leakage of sensitive plaintext. Although still in relatively common use, there

8428-410: The reverse function; it converts a digital signal into an analog signal. An ADC converts a continuous-time and continuous-amplitude analog signal to a discrete-time and discrete-amplitude digital signal . The conversion involves quantization of the input, so it necessarily introduces a small amount of quantization error . Furthermore, instead of continuously performing the conversion, an ADC does

8526-930: The same current must leave a node as enter it, and since the impedance into the (−) pin is near infinity per assumption 2, we can assume practically all of the same current i flows through R f , creating an output voltage V out = V in + i R f = V in + ( V in R g R f ) = V in + V in R f R g = V in ( 1 + R f R g ) {\displaystyle V_{\text{out}}=V_{\text{in}}+iR_{\text{f}}=V_{\text{in}}+\left({\frac {V_{\text{in}}}{R_{\text{g}}}}R_{\text{f}}\right)=V_{\text{in}}+{\frac {V_{\text{in}}R_{\text{f}}}{R_{\text{g}}}}=V_{\text{in}}\left(1+{\frac {R_{\text{f}}}{R_{\text{g}}}}\right)} By combining terms, we determine

8624-504: The signal can be reconstructed. If frequencies above half the Nyquist rate are sampled, they are incorrectly detected as lower frequencies, a process referred to as aliasing. Aliasing occurs because instantaneously sampling a function at two or fewer times per cycle results in missed cycles, and therefore the appearance of an incorrectly lower frequency. For example, a 2 kHz sine wave being sampled at 1.5 kHz would be reconstructed as

8722-406: The subtraction processes. Wilkinson ADCs have the best linearity of the three. The sliding scale or randomizing method can be employed to greatly improve the linearity of any type of ADC, but especially flash and successive approximation types. For any ADC the mapping from input voltage to digital output value is not exactly a floor or ceiling function as it should be. Under normal conditions,

8820-401: The terminals, either peak-to-peak or RMS as required. So we see v c , v e , and v b , as well as i c , i e , and i b . Using these conventions, in a common-emitter amplifier, the ratio v c / v b represents the small-signal voltage gain at the transistor, and v c / i b the small-signal trans-resistance , from which the name transistor

8918-415: The time it takes to charge (and/or discharge) its capacitor from 1 ⁄ 3   V supply to 2 ⁄ 3   V supply . By sending this pulse into a microcontroller with an accurate clock, the duration of the pulse can be measured and converted using the capacitor charging equation to produce the value of the unknown resistance or capacitance. Larger resistances and capacitances will take

9016-550: The time to charge the capacitance from a known starting voltage to another known ending voltage through the resistance from a known voltage supply, the value of the unknown resistance or capacitance can be determined using the capacitor charging equation: V capacitor ( t ) = V supply ( 1 − e − t R C ) {\displaystyle V_{\text{capacitor}}(t)=V_{\text{supply}}\left(1-e^{-{\frac {t}{RC}}}\right)} and solving for

9114-510: The two golden rules : The first rule only applies in the usual case where the op amp is used in a closed-loop design (negative feedback, where there is a signal path of some sort feeding back from the output to the inverting input). These rules are commonly used as a good first approximation for analyzing or designing op-amp circuits. None of these ideals can be perfectly realized. A real op amp may be modeled with non-infinite or non-zero parameters using equivalent resistors and capacitors in

9212-576: The typical V S = ±20 V, the standing current in Q11 and Q12 (as well as in Q13) would be ~1 mA. A supply current for a typical 741 of about 2 mA agrees with the notion that these two bias currents dominate the quiescent supply current. Transistors Q11 and Q10 form a Widlar current mirror , with quiescent current in Q10 i 10 such that ln( i 11  / i 10 ) = i 10  × 5 kΩ / 28 mV, where 5 kΩ represents

9310-411: The unknown input voltage to the input of an integrator and allows the voltage to ramp for a fixed time period (the run-up period). Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero (the run-down period). The input voltage is computed as a function of the reference voltage, the constant run-up time period, and

9408-471: The unknown resistance or capacitance using those starting and ending datapoints. This is similar but contrasts to the Wilkinson ADC which measures an unknown voltage with a known resistance and capacitance, by instead measuring an unknown resistance or capacitance with a known voltage. For example, the positive (and/or negative) pulse width from a 555 Timer IC in monostable or astable mode represents

9506-418: The useful resolution of a converter is limited by the signal-to-noise ratio (SNR) and other errors in the overall system expressed as an ENOB. Quantization error is introduced by the quantization inherent in an ideal ADC. It is a rounding error between the analog input voltage to the ADC and the output digitized value. The error is nonlinear and signal-dependent. In an ideal ADC, where the quantization error

9604-433: The whole passband of the converter. If a signal is sampled at a rate much higher than the Nyquist rate and then digitally filtered to limit it to the signal bandwidth produces the following advantages: Oversampling is typically used in audio frequency ADCs where the required sampling rate (typically 44.1 or 48 kHz) is very low compared to the clock speed of typical transistor circuits (>1 MHz). In this case,

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