# 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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### 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 ...
3answers
310 views

### 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 ...
2answers
35 views

### Error: Multiple analyses requested in LTSpice

I am running the following simulation in LT spice but I am getting the following error: Multiple analyses requested .trans 0 100m 90m 1m .op Here is my circuit. ...
1answer
65 views

### Current Mirror Controlled Switch

I'm trying to understand how Vg is calculated in this circuit below. I understand the current mirror is meant to protect the SMPS from current flowing into the output of J2 if the 12V source is not ...
1answer
46 views

### The load resistance in a MOSFET current mirror vs CMOS

In class I have learned that in a MOS current mirror like the one below, we can say that the load seen by M1 is equal to r_o of M2. This makes sense to me since I have drawn the small signal model and ...
1answer
74 views

### How do I find CMRR?

How do I find the common-mode rejection ratio, CMRR for this circuit? I know I have to find differential gain and common-mode gain as 'differential mode gain/commonmode gain' but with current mirrors ...
2answers
101 views

### 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 ...
1answer
86 views

### Question about diode connected transistor (BJT) with current source

I'm trying to find ΔV for this circuit, but I'm having a bit of trouble doing so. I think the current on the right BJT will be n times greater than the left, but I'm not sure about that either. It ...
1answer
54 views

### Potential In VA

I'm trying to find VA and I don't get something, is Ic1 = V+/20k, and then this current splits through emitters of Q1 and Q2? If so, then the voltage VA is 0? Also, I know that Q3 and Q4 are a ...
2answers
84 views

### 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 ...
0answers
38 views

### Op-amp with voltages in both inputs

I'm trying to solve a practice problem, which is represented by the schematic below. simulate this circuit – Schematic created using CircuitLab We are asked to relate the voltages $V_1,V_2$ ...
2answers
228 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 ...
0answers
164 views

### Low-voltage cascode current mirror biasing circuit

On the left is a low voltage cascode current mirror and on the right is a circuit whose left branch generates $V_b$ for the mirror. Razavi (Design of Analog CMOS Integrated Circuits 2nd edition, ...
1answer
108 views

### Huge current mirror circuit

I have a question about the circuit above. In the first place we can measure the current IR2 in given values, then using the current mirror topologies we can express IC7, IC8, IC3, IC11 and the other ...
0answers
54 views

### High Power BJT Current mirror

I am trying to find an example of BJT current mirror with high power consumption. Any advice concerning the setup , or an example design will be appreciated.
0answers
79 views

### Simple MOSFET current mirror, Cascode Current Mirror, Impedance and Output Voltage Swing

Sorry if I don't format this exactly correct, this is my first post on this site. I am working with a simple MOSFET current mirror and a cascode current mirror and need to determine the output swing ...
0answers
73 views

### what is current mirror?

I was looking for a high-level explanation about the current mirror but couldn't find it. Can someone explain what is current mirror using simple words? What does it do? and what is the real ...
1answer
78 views

### 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 ...
2answers
339 views

### BJT Current Mirror Problem

Problem: A simple current mirror is set up with two NPN transistors. $V_{CC}=12$ Volts $+V_{in}= 30$ Volts. Load resistance $R_L\ =\ 1\ K\Omega$. What is the resistance value interval for ...
2answers
177 views

### 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 ...
3answers
85 views

### Built difference amplifier “tail” vs. SPICE models

I am working on a difference amplifier example lab 5L.1 from Art Of Electronics Hands on Lab Course (I am not a student). I simulated three types of "tail" circuits using SPICE. Then I built ...
1answer
78 views

### Differential Amplifier - Active Load Current MIrror Logic

I'm trying to wrap my head around the workings of a differential amplifier when a current mirror is used as an 'active load' With reference to this Youtube video leecture: here My understanding so ...
3answers
387 views

### 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 ...
1answer
75 views

### Current mirror collector voltage

I'm trying to get the VGS of DMHC4035PMOS. Based on the simulation, I'm supposed to get -5.53V but I'm getting -8.2V on my PCB. Is there anything wrong with the design? What is the collector voltage ...
0answers
50 views

### A kind of current mirror design

Recenlty I saw a kind of current mirror circuit used to provide bias current for a differential amplifier. The circuit is posted below and I don't understand its working mechanism, as well as the ...
3answers
79 views

### MOS current mirror region of operation

The mosfet M1 is clearly in saturation as gate and drain terminals are shorted. Why we take M2 also in saturation? I know Vgs1 = Vgs2 and they are identical MOS but i cant justify why M2 should be in ...
3answers
181 views

### Is the transistor Q4 in the wide swing cascode current mirror operating in linear region?

In the wide swing cascode current mirror shown below, the transistor Q4 is in the linear region of operation according to the voltages at gate and drain. Is it not necessary for transistor to operate ...
3answers
240 views

### 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?
2answers
140 views

### 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 ...
0answers
37 views

### 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, ...
1answer
227 views

### 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, ...
1answer
87 views

### DC voltage at the output of push pull stage

I have an output stage. The circuit diagram is as shown: In DC condition, the node X has a DC voltage of Vdd/2. The node Z has a voltage of about 1.26 volts. Vdd = 3.3 volts. Transistors M7 and M5 ...
1answer
58 views

### Modified Current mirror principle

Could somebody explain to me the principle of this current mirror? I don't understand why I throughout my R2 and R3 is not dependent on R1 (R bias)? My goal is to have 0,8V voltage drop on R3. Many ...
0answers
53 views

### Transistor amplifier with active load in high frequencies

I have simple transistor amplifier with active load, problem is I am using the circuit in 1 to 10 MHz range, so as you can see the gain is low in this region. Used transistors are bc337 and bc327. I ...
0answers
32 views

### bipolar current mirror, unified control

I'm trying to obtain a high impedance, several decades current pump for charging a capacitor from 1uA to 10mA, swing +/-5V. I arranged two current mirrors like this and is working acceptable for ...
1answer
669 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 ...
0answers
41 views

### Current Mirror - Supply Dependence

I have a question about one of the current mirrors introduced in the "Bandgap References" chapter of Razavi's Design of Analog ICs. He has this: My confusion is about Equation 12.1. I know that ...
1answer
92 views

### How to measure amplitude MHz sine wave with 50 volts common mode

For a resonant switching power application I need to measure the amplitude of a differential signal that is a sine wave with frequency between 1 and 2 MHz, and amplitude up to about 2 volts. There is ...
2answers
122 views

### 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 ...
1answer
211 views

### temperature stability in current mirrors

I have read here that temperature stability is one of the performance issues in current mirrors. Can anyone what does temperature stability mean in current mirrors? Thanks.
2answers
205 views

### Why my current mirror results in wildly different currents?

Let me start with that I'm new to current mirrors and my idea may be conceptually wrong. Feel free to ask any clarifying questions. I'm designing a dual "LED lamp" with very finely tunable brightness ...
0answers
125 views

### controlling a sinking current with a positive voltage

I have found current mirrors like the basic one below often very useful. obtained from https://www.electronicsnotes.com/articles/analogue_circuits/transistor/current-mirror-circuit.php However, ...
1answer
90 views

### Is this current source (or mirror)? How does it work?

I'm trying to understand this schematic of this differential probe: There are several things I do not fully understand. One of them is this section: I would guess it is a constant current source (or ...
1answer
75 views

### Is there any way to match Vth of 2 mosfets with different aspect ratio?

For the floating mirror circuit to work properly, the threshold voltage of M1 and M2 must be the same. However, (W/L)1 ≠ (W/L)2. So I thought to get a first order matching I can match L1 and L2 (to ...
2answers
112 views

### 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 ...
1answer
49 views

### Mos circuit amplifier with multiple stages , overall gain

I have the following circuit and i am trying to find uin/vout. My thought process is that M3-M4 is a Cmos inverter so i can calculate the gain until that point as A1= -gm3(ro3//ro5) How can i find the ...
1answer
190 views

### 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 ?
1answer
383 views

### Finding Wilson Current Mirror Output impedance

I am trying to confirm my output resistance calculations with my simulation. How can I measure the output resistance seen by Q4 in order to confirm my calculations? How I measured $r_{o2}$ (image ...
1answer
143 views

### Measurement of output impedance (ro) of a modified wilson current mirror

How do I measure the small signal output impedance (ro) of a modified wilson current mirror? example Q4:
0answers
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### MOSFET current mirror with compensation

I am trying to understand the difference between a MOSFET current mirror with and without compensation (Replace Q3 with a short circuit). In the case of a current mirror without compensation, V1 ...