# 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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### 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 ...
29 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 ...
66 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 ...
72 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 ...
29 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.
87 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 ...
19 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, ...
59 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 ...
50 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 ...
71 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 ...
45 views

### Simulating a specific LED on Eagle through NgSpice

I was trying to simulate a current mirror circuit for a parallel set of LEDs in a project that I am undertaking. However, before actually working with real parts, I wanted to simulate the circuit in ...
40 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 ...
24 views

### Split collector current mirror [duplicate]

I'm familiar with the basic current mirror, as below: simulate this circuit – Schematic created using CircuitLab However, having recently learned about split collector BJTs, I wonder if a ...
67 views

### Excessive Op-Amp Settling in Exponential Converter

This circuit converts a linear voltage to exponential current for controlling the frequency of a VCO. It simulates without issues, and almost works, but there is a huge amount of settling on the ...
93 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 ?
126 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 ...
63 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:
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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 ...
43 views

### Mosfet current mirror maximum value of load resistance to operate in saturation region

Let's say we have a current mirror with these parameters. I calculated current through resistor IR and VOUT voltage. But there is a question like that. What is the maximum value of (in Ohms) that ...
96 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 ...
65 views

### Ground-referenced current mirror with low voltage drop

The following circuit produces a voltage v2 that is the logarithm of I[dut]. I've modeled it with I1 ranging from 1uA to 100mA and it does essentially what I want, but it could stand some improvement:...
343 views

### Small signal analysis of current mirror

I have problem getting the output resistance of this current mirror. How should I draw the small signal circuit and derive the output resistance equation?
114 views

### Weird Current Mirror

I just encountered this circuit and I'm a bit confused by it I see that it's an NMOS current mirror. At first I thought it's a cascode current mirror due to M3 on the right but it isn't. I have two ...
276 views

### Output voltage of MOSFET differential pair with current mirror load

I've seen this circuit from https://www.allaboutcircuits.com/technical-articles/advantages-of-the-actively-loaded-mosfet-differential-pair/ How are the drain voltages equal?? I can't seem to figure ...
201 views

### 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 ...
95 views

### How to calculate the output voltage of the mirror circuit?

Please refer the following circuit added. Output voltage (Vout-A) is measured as follows, Following is the way I have started analysis: Krichhoff's voltage law around the loop ( R12 -> R3 -> V_BE(Q2)...
62 views

### Current mirror with source resistance

In the book i=2 ma is given I can get this ans by solving equations but how to intutively prove that the current would be same?
103 views

### 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 ...
161 views

### Current booster/amplifier for OTA

I am designing an Operational Transconductance Amplifier whose maximum output current should be 15mA. Using Super Class AB amplifier, I was able to get a maximum output current of up to 2mA. The ...
133 views

### Current mirror and differential amplifier problem

take a look at this circuit: I have a problem with calculating $I_{out}$, or, more likely, understanding how this circuit works. I know that $I_{out}=I_{C4}-I_{C2}=I_{C1}-I_{C2}$, but what is the ...
2k views

### output resistance of current mirror

I am being asked to find the output resistance of the current mirror below. the correct answer is supposed to be R_out = 103k ohms. but when am simulating the circuit, I get R_out = 3.82k ohms. Can ...
203 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 ...
76 views

### Design of a differential pair

simulate this circuit – Schematic created using CircuitLab Problem: I need to design a differential pair with a gain of 30dB To make this design I have to used 4 mosfets transistor 2n7000 with ...
605 views

### Output Impedance of a Wilson Current Mirror

Is the ideal output impedance of a Wilson Current Mirror 0? Also, in the formula for the actual output impedance of Wilson Current Formula (i.e. R_out = [B/2]* r_o), what does r_o stand for? Also, ...
302 views

### 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, ...
556 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 ...
64 views

### Working out ICopy from a current mirror [Mosfet]

I'm trying to solve for $I_{copy}$, but I've looked around on the internet and cannot find an explanation. However, I know the formula: $I_{copy} =\frac{I_{REF} * W_1/L_1}{W_{REF}/L_{REF}}$ ...
594 views

### Wide Swing Cascode Current Mirror Biasing Difficulties

I'm working on designing a cascode current mirror, depicted below: Constraints: all Von needs to be above 200 mV, all Vds neds to be at least double Von, L is 0.35 um. Derived from the SPICE file, k'...
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### Basic Current mirror using BJTS

Hi, I'm fairly new to BJTs and I've been trying to analyze the above basic current mirror to prove that $$I_{ref} = I$$ (aproximately), but have gotten nowhere. I have attached where I've gotten so ...
217 views

### How does a current mirror produce an amplified current? What is the physical process behind it?

I know that the MOSFET based current mirror gain is equal to $\frac{I_O}{I_{ref}} = \frac{\frac{W}{L}2}{\frac{W}{L}1}$. To get the output current, $I_O = I_{ref}\frac{\frac{W}{L}2}{\frac{W}{L}1}$, ...
192 views

### Improved Differential Amplifier

I made this circuit as shown below: simulate this circuit – Schematic created using CircuitLab After those improvements with current mirror and constant current source were considered, this is ...
1k views

### Noise in current mirror

In most CMOS applications, the use of resistive source degeneration to reduce noise and improve matching is restricted due to headroom constraints. A) Could anyone elaborate on this statement ...
342 views

### Improved current mirrors

I do not understand "The circuit on the right is a feedback amplifier with loop gain T. Since all time constants in that loop are of the same order of magnitude, they create a system with several ...
463 views

### How does the voltage difference develop when MOSFET is biased with Current Source?

I have a circuit in LTSPICE which is performing as desired but I could not understand the working of it. Basically I have an NMOS circuit shown below (fig a): Here are some values which I calculated ...
2k views

### Cascode Current Mirror, Minimum output voltage

I can say that I understand simple current mirrors fairly well, but what i do not understant is the minimum output voltage requierd for the circuit to work properly...for the transistors to be in ...
923 views

### current mirror as active load in common emitter amplifier

Could someone help to analyse the circuit above, which is a single common emitter amplifier. And for the purpose of larger voltage gain, a current mirror building block is applied as active load. But ...
202 views

### 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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### The current of M5 and M7 of two stage OTA

Let direct current = 100μ,i know the drain current of M3=M4=M6=M1=M2=100μ My question : Is the drain current of M8=50μ ? Oμ ? i think drain current will flow to the gate of M8 dircectly ...
The transistors have finite β and an infinite early voltage. Derive the expression for $I_0$ in terms of $I_{REF}$and β. In this question Io has to be represented in terms of $I_{REF}$.......