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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Why the extra transistors in this current mirror?

I'm trying to understand the unusual current mirror circuit below. The current controlled by R2 is mirrored to R1. The strange feature of this circuit is that Q1's collector and base aren't connected ...
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Electret Microphone Preamp Circuit

The following electret microphone preamp circuit seems to work pretty well. My electret model is a little off because on the bread board R6 needs to be ~33k to get the output at 1/2 supply. Just a ...
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Current mirror biasing circuit

I have just seen the comparator as figure 1 below and I am wondering why don't we use a simplified version as figure 2? Hope anyone could make it clear. Thanks. Figure 1: Figure 2: simplified ...
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How this current mirror act as a replacement to resistor Rc?

In this differential amplifier: The PNP transistor Q6 acts as an active load resistor and as a current mirror. Since current source Q6 has nearly infinite impedance, we will be able to have very ...
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929 views

Improve rise-time of NPN current mirror

I'm looking for a way to improve the rise-time of a current mirror. My problem is as follows: I want to interface with an obscure single wire protocol. I'm starting with a digital signal that has a ...
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Can Dual BJT packages be reliably used as Current Mirrors

Say I need current mirrors, can I just use Dual NPN packages? I know that if multiple BJTs are manufactured in a die, they can pretty much be guaranteed to have the same spread. Or, should I just ...
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BJT differential amplifier output saturation

I'm making a long-tailed pair amplifier using a current mirror, the circuit has the following layout: I simulated it on PSpice and it worked, you can see the bias here: I tested it in the real ...
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Finding Rout of differential pair with active current mirror (from Razavi's “Design of Analog CMOS Integrated Circuits 1st Edition”)

According to Razavi, \$R_{out}\$ is approximately \$r_{o2}||r_{o4}\$: I get the same answer (assuming \$2r_{02} >> \frac{1}{g_{m3}}||r_{o3}\$): But how did he get equation 5.27? In particular, ...
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Current Mirror Gain 1.5 with discrete components

I was trying to simulate the circuit mentioned in https://wiki.analog.com/university/courses/electronics/text/chapter-11 under paragraph 11.4.1. I need to make a current amplifier with a current gain ...
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132 views

Experimental feedback scheme in DC-DC boost converter

Does anyone know if it's possible to connect the feedback pin of a DC-DC boost converter chip like Texas Instruments' LM2733 in a different manner than the one described in the datasheet, namely on ...
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Widlar current source

I need help solving this problem. I believe the current in the left side of the circuit equals the current in the right side. Therefore, $$K(V_{gs1} - V_t)^2 = 4K(V_{gs2} - V_t)^2$$ I also know \$V_{...
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Confusion about a basic BJT current mirror

Below is part of a BJT current mirror: I marked the specific nodes of the reference transistor on the left as x, y and z. Many texts claim the following(I tried to summarize): Since the collector ...
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649 views

Current mirror: is there a name for this NPN-PNP pair, and how does it work?

I'm looking at the schematic for the MC1460 voltage regulator. At the top it has three current mirrors, each with an NPN-PNP pair. Is there a name for that transistor structure? These pairs look like ...
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Current mirror improvement by adding resistors

One of the limitations of the current mirror with 2 BJTs is the Early effect. According to the Art of Electronics 2nd Ed., adding emitter resistors should make the circuit "a far better current source"...
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Supply voltage in a current mirror necessary?

Consider the current mirror below (circuit taken from [Razavi]). I wonder about the \$ V_{DD} \$ in the circuit. No matter if its there or not, \$ V_{GS} \$ of M1 stays the same and therefore also \$ ...
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Why do we use current mirrors?

Sorry if the question seems stupid, im not much into electornics just trying to get into it... I'm trying to figure out the purpose of current mirror, I read everywhere that it copies reference ...
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What is the use of the line connecting drain and gate in current mirror using voltage bias?

I am confused about current mirror. Given this circuit simulate this circuit – Schematic created using CircuitLab it makes sense to connect the drain to the gate in order to make their voltage ...
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Why does the “top” transistor in a cascode not set the current?

This has been bothering me for some time. Why is it that the overdrive voltage of the bottom transistor in a cascode controls the DC current, and not the Vgs of the top transistor? Similarly, in an ...
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Constant-gm bias circuit

I am doing a study on Improvements in biasing and compensation of CMOS opamp. Do you guys know how to come up with the equation for RDS4C ?
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output current of Wilson mirror

I am trying to drive the output current Iout but I am not getting what it is shown on the graph. Can you have a look and let me know what I got wrong please? Thanks here is my attempt
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Current mirror configuration analysis in LM393

I've been trying to figure out how this comparator (LM393) works. So far I can recognize the sections: Q8, Q9, Q10, Q12 form the differential amplifier. Q15 and Q16 are the output transistors. Q1, ...
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832 views

Input stage of a current mirror circuit

I'm trying to understand current mirror circuits and I've been reading this article. I'm unable to understand the input part of the circuit where the author says "Producing the opposite where the ...
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Is \$V_A\$ or \$V_B\$ the inverting input here?

Is \$V_A\$ or \$V_B\$ the inverting input and why?
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Current Mirror Circuit

Below is a sample current mirror circuit. I understand that If the transistor Q1 is connected in a diode connected BJT configuration and the Transistor Q1 and Q2 have identical transistor parameters, ...
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High-Swing Cascode Current Mirror

I am currently dealing with current mirrors and came across the circuit shown below, a High-Swing Cascode Current Mirror. I read that this implementation, as the name suggests, has the advantage of a ...
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MOSFET current mirror: Saturation mode?

I have some trouble understanding why M1 is in saturation/active mode. According to Wikipedia a MOSFET is in saturation mode if \$V_{GS} > V_{th}\$ and \$V_{DS} \ge (V_{GS} – V_{th})\$. However ...
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What is the point / name of this circuit? Reverse voltage protection + current mirror?

I stumbled across this circuit on page 8 of the Nano Pi Duo 2. What purpose does it serve? I recognize the MOSFET arrangement to be a reverse voltage protection circuit and the PNP transistors form a ...
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Problem in the output current of an PNP current mirror

I have a problem in the implementation of a current source, based on an OPAMP voltage-to-current converter followed by a PNP current mirror (see picture). Indeed, the output currents are identical to ...
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In a Wilson mirror, does Q3 need to have the same beta to cancel the base current error?

I'm learning about Wilson mirrors in the Art of Electronics Third Edition (pg. 102). It shows the following circuit: simulate this circuit – Schematic created using CircuitLab It then explains ...
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1answer
714 views

How does this circuit compensate for current hogging?

In The Art of Electronics by Horowitz & Hill, there’s a section about current mirrors with multiple outputs. We're then given the following circuits: It's then described how the circuit shown in ...
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686 views

Current source improves linearity on collector BJT

I'm learning about analog electronics. I'm looking into amplification stages at the moment. Question 1: Single BJT C-E Amplifier. Usually you put a resistor between collector and V++, so as \$I_b\$ ...
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200 views

Differential pair active load contradiction

I'm confused about one current-based explanation for why the active current mirror restores a differential pair's gain by letting each differential input reinforce the other. The explanation (from ...
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Implementation of Current Source for a Current Mirror

let's consider this simple example of current source: It is a current source because each load I connect to it, it will receive a value of current equal to Vbias/R, which does not depend on the value ...
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Using a current mirroring source to power 6 Nixie-Tubes

I would like to drive 6 Nixie-Tubes from a standard USB-Port (500mA / 2.5W), which is somehow hard to do because \$ 190 \text V \cdot 3 \text{mA} \cdot 6 = 3.5 \text W\$. If I could reduce the source ...
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Current mirrors as active loads in BJT differential amplifier, what does that mean?

I have seen current mirrors being used as current source in differential stage of an amplifier design. The reason given is that the current mirror has a very high output impedance and behaves like an ...
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287 views

Gate Source Voltage Drop Approximation

When dealing with BJTs in an approximate large signal analysis, Vbe is often chosen to be 0.7 Volts (Given the component is operating in active mode). My question is: Is it possible to do the same for ...
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How does a cascode current mirror maintain equal Vds of the bottom transistors?

A basic current mirror is shown below: The load and reference current relationship is affected by channel length modulation: In order to cancel the effects of channel length modulation, vds1 and ...
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320 views

~40 uA current sink… what current mirror topology to use?

I need to sink a constant 20-60 microamps from the inverting input terminal of an op-amp in order to shift the output voltage upwards a bit. This is a pretty low-speed circuit, with little spectral ...
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1answer
769 views

MOSFET Sizing in Wide-Swing Current Mirror Design Exercise

TL:DR How do I know how to size transistors? This is the same problem as this one. Now knowing that I can change L, I know that my W/L ratio to make Von = 200 mV is roughly 6.75. Also knowing that ...
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How does this circuit given with diode works different from the standard current mirror circuit or will it work in the same way? [duplicate]

This question had already been asked here by someone else few years ago but I could not see any satisfactory answer so I am asking it again. All I can see relevant in that post was the image attached ...
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What is the ground-source voltage of this current mirror?

In Neamen's microelectronic book, there's a problem using this current mirror There is a 5V DC voltage source above the current source. The reference current is 250 microAmp. The threshold voltage is ...
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Beta multiplier reference

In the beta multiplier reference circuit, what is the function of start-up circuit? Can we use the beta multiplier without the start-up circuit?
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Limitations of MOSFET-pair Current Mirrors

simulate this circuit – Schematic created using CircuitLab For simple MOSFET-pair current mirrors, such as the NMOS version above, are there any known disadvantages that one has to consider? ...
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Matched biasing transistor vs. emitter resistor in current mirror

If adding emitter resistors can reduce the temperature variation in \$V_{BE}\$, why do we still need to find a matched pair of transistors to construct a current mirror?
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Can anyone explain these conditions for the current mirror?

An important feature of the current mirror is a relatively high output resistance which helps to keep the output current constant regardless of load conditions. Another feature of the current mirror ...
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Specific current mirror explanation-source

I am trying to understand the following current mirror, though I haven't found any book that describes it. Is there any source in which I can see how it works and its pros and cons? The drawing is ...
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862 views

Question about the 3-transistor current mirror

This is a basic 3-transistor current mirror: I see some circuits add an extra resistor from emitter of Q3 to \$V^{-}\$. Just like this: What's the purpose of this resistor?
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Current mirror with multiple outputs

For my new amplifier design I need a kind of parallel Norton level shifter for differential signal (to subtract the same externally controlled voltage drop from two signals). One possibility is to use ...
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Designing a MOSFET current mirror circuit

This is the design problem: This is a brief of my design for W and L of the transistors and R: I've connected the upper voltage source to ground and made the lower one equal to 0.4 V to make sure ...
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Why is the output current not equal to the input current in this current mirroring circuit?

Why is the output current not equal to the reference current in this current mirroring circuit? (I have been explicitly told that they are not equal). Both of the transistors are equal and in the ...