# Questions tagged [current-mirror]

Current mirror circuits enable the mirroring of the current flowing somewhere else in the circuit onto a path of interest. Typically used in non intrusive load current measurements.

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### How to solve current mirror with emitter degeneration

These circuits/discussion are from Art Of Electronics by Paul Horowitz & Winfield Hill, 3rd Edition, Figures 2.58 & 2.60. Assumptions: $Q_1$ & $Q_2$ are matched, disregard base ...
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### Output current increase in a cascode current mirror

I have been studying a cascode current mirror for an electronics class, that follows this configuration: As I increase the output voltage Vd4, for most of the sweep the behavior is as expected, but ...
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### RC high-pass filter is blocking all current instead of just removing the DC offset

I am trying to simulate a simple current mirror, which accepts an AC current with a DC offset making the entire signal positive, so that it is properly mirrored (the signal was being cut off for ...
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There is a requirement for a P-side current generation. Currently we have P-side Vt/R solution which is the left branch in the figure, except it is diode connected. When the PMOS is diode connected, ...
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### Negative feedback amplifier

The following circuit diagram is from a book on electronic circuits. The Current source $I_s$ is driver of the amplifier. It was written that this amplifier has negative feedback. It seems that if ...
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### Convert linear output of current mirror to exponential

I am currently trying to change the output from my current mirror, which is linear, to a more exponential one. The picture below shows the current mirror I'm using, which is intended to work from 8 to ...
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### LM3900: different input impedances in symmetric pins?

Referring to the LM3900 "Quadruple Norton Operational Amplifiers" datasheet, consider the schematic of each single amplifier at page 1. simulate this circuit – Schematic created using ...
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### Disconnecting load circuit from reference [current mirrors]

I have started learning microelectronics design and I am currently working on my bachelor thesis. There's one thing I wanted to ask you about current mirrors and its switching. My thesis is mainly ...
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### Why is collector current in a diode-connected transistor not subject to the non-ideality of the B-E junction that it must necessarily traverse?

In a recent comment I was asked why a diode-connected transistor behaves as it does. Jonk's answer here addresses this question, and explains that the geometry of the B-E junction in a signal BJT ...
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### For a degenerated CS amp with current mirror would the small signal model include the current mirror

I am aiming to create an actively loaded degenerated CS amplifier and analyse the small signal performance in relation to maximum signal levels, maximum signal swing, voltage headroom requirements, ...
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### M1 and M3 are connected in OTA, but in (a) they are separated. The author thinks they're equivalent. Why?

The following is from the book Design of Analog CMOS Integrated Circuits, page 147. M1 and M3 are connected in OTA (operational transconductance amplifier), but in (a) they are separated. The author ...
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### How is this a current mirror?

This article is talking about floating an IC's GND to use it at a common mode voltage higher than it is rated for. It then says it level shifts the IC's current output to ground by using the Q1-Q2 ...
1 vote
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### Cascode current mirror transistor biasing

I'm having trouble intuitively understanding how a MOSFET cascode current mirror functions. I understand that the purpose of M3 is to shield M2 such that variations in applied voltage do not affect ...
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### Why doesn't current flow to ground in some circuits? (followup question)

This is a follow-up question to the following questions: Why doesn't current flow to ground in some circuits? When does and when doesn't current flow to ground? I have no issue accepting the ...
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### Measuring output impedance of Widlar current source

I have designed the circuit shown below for a reference current of approximately 1mA and an output current of approximately 100uA. I have observed that I am able to supply approximately 100uA to load ...
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### Why isn't my current mirror reflecting 500uA on each side?

I'm designing a telescopic cascode with a tail current source of 1mA. I had set my VDD to be 2V and all of the mosfets in the schematic seem to be saturated but the current reflected by the current ...
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### Need clarification regarding op-amp's ground/ reference and common mode dependence on supply

I am confused about several aspects pertaining to op-amp DC biasing and its effects on ground/common mode limits. The more I read about this, the more muddled up I get. I will try to frame my queries ...
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### Early effect in simple current mirror

By "simple current mirror" I mean the following circuit. Due to the Early effect the output current changes to some degree with output voltage. According to The Art of Electronics (3rd ...
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### Wilson BJT current mirror output impedance

I am trying to have a small signal analysis of a Wilson BJT current mirror to find out what is the output impedance. Already I know that the answer is $$R_o=\beta r_o/2$$ In the first step, I need to ...
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### Is a current mirror necessary if LEDs are binned?

I have a 20VDC input with a buck CC LED driver, driving 48 LED strings of 6 x 3V LEDs in series. I am underdriving the LEDs at 60% of rated power. Each LED string consumes ~33mA. The LEDs are ...
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### How does the attack / release element of this audio compressor function?

This is an audio compressor circuit based on (and designed by the makers of) the THAT 4301. U2B converts the AC input to RMS, which is then inverted by U2D. When there is no signal input to the ...
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### How does current flow when you short base and collector in a current mirror?

I am studying analog electronics and I don't understand how current flows in a current mirror when you short base and collector together. Electrons are being injected from the emitter into the base ...
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### Diode-connected BJT vs base-emitter BJT diode vs diode

I was having a look at the circuit design of Keithley 236 SMU. You can find this part of the circuit in the Keithley 236 Service Manual. Q47 is a BJT. Only the base and emitter are connected, which ...
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### Constant current power supply and 4 unique loads that I would like to individually control via PWM. Loads are to be driven at varying currents

I have a 1400ma constant current power supply (plenty of power to drive all loads at 100% duty), and I want to PWM 4 separate loads that are all driven optimally at either 350ma, 700ma, or 1400ma. The ...
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### How does the current mirror stabilize tail current in an op amp?

Op amps often use the "slave" side of a current mirror to provide the tail current for the input transistor pair, such as in this simple op amp voltage follower schematic: The "gates&...
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### Why this 4-bjt current miror got better precicion?

I just wonder how precise of 2-bjt current mirror circuit then I found this circuit from link form circuitlab.com My question is How much we can rely on 2-bjt how to determine how precision there ...
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### Designing current mirror

I have a 105V/3A output current source, and I am trying to get a current mirror circuit to pass 10-100 uA DC across 5 lanes that have very high impedance (around 1 MOhm). What is the best/quickest way ...
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### Can't understand how the Zener voltage reference works

I've built a small amplifier circuit in which I've wanted to use a Zener diode as a reference but I can't figure out how it works. Knowing that the negative rail is -5V and the Zener breakdown ...
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### How to drive dozens of LEDs with the same current without a constant current LED drive IC?

Let's say I have an array of many indicator LEDs that I need to turn on/off independently; the LED current is about 1 mA. In the past I used constant sink LED driver ICs such as the TLC5916 as shown ...
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### How can a current mirror be adjusted to create a ratio between the reference and the output current?

I am working on a project were I need to pass a current through a load and a larger multiple through a different load. Hence if I pass 100mA through this load I need to pass approx 10A through the ...
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### Voltage Controlled (w/ op amp) Wilson Current Mirror Can't Actually Mirror (Missing something)

I'm working on a current mirror circuit and I'm in a little bit of a problem. I have a current mirror circuit, which is supposed to, well, mirror the current, except that the current in the "copy&...
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### Long tail amplifier using current mirrors

I have built this in the Multisim simulator and it works there as desired. Now I have built it on a "lame" breadboard. Is the upper PNP current mirror correct? Since the "left" ...
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### Can current mirror branches be connected to different sources

Can the branches within a current mirror be connected to different sources as shown below? The aim is to provide the high voltage required by each LED but reduce the voltage across the resistor R1 in ...
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### How to ensure the correct supply voltage when using a current mirror

I am trying to design a current mirror with a constant current source and 2 parallel LEDs (I have to connect the LEDs in parallel and cannot use a separate current source for each LED). If each LED ...
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### Will a current mirror prevent thermal runaway of these LEDs in parallel

The source is a constant current LED driver. I found that connecting the LEDs in parallel caused thermal runaway with one LED consuming nearly all of the current with its temperature constantly ...
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### Why use diode connected BJT (and not just connect two BJT back-to-back) for current mirror circuit?

I have been studying about current mirror circuits using BJTs. The circuit I have is this: For the left BJT, it says: IC1 = Io(e^(Vbe1/Vt)) This is understandable ...
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### PMOS current mirror acting wonky in Simscape

I am trying to model a current mirror, seen below, solely built upon PMOS. This should not be a hard task because the theory and implementation are straightforward. What I do get when I model it in ...
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### Qualitatively and quantitatively finding the transient response of a current mirror

In a current mirror circuit, when Iss is doubled or multiplied by a factor, it takes some time to clone those values and reach the steady state. I varied the width of the transistor and found that the ...
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### Current mirror LED circuit with constant current source

I am trying to temporarily fix a current mirror circuit for driving 40 LEDs. Each LED in the circuit represents a custom LED strip that has a forward voltage of roughly 145V and a forward current of ...
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