# 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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0answers
571 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?
2answers
138 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 ...
1answer
395 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 ...
0answers
314 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 ...
0answers
116 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)...
2answers
71 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?
2answers
183 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 explains ...
1answer
207 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 ...
1answer
327 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 ...
3answers
5k 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 ...
1answer
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 ...
0answers
98 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 ...
1answer
1k 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, ...
2answers
373 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, ...
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 ...
1answer
81 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: $I_{copy} =\frac{I_{REF} * W_1/L_1}{W_{REF}/L_{REF}}$ ...
2answers
827 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'...
1answer
85 views

### 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 ...
2answers
258 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, $I_O = I_{ref}\frac{\frac{W}{L}2}{\frac{W}{L}1}$, ...
1answer
248 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 ...
1answer
2k 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 ...
1answer
481 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 ...
1answer
658 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 ...
1answer
3k 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 ...
2answers
1k 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 ...
3answers
265 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 ...
2answers
170 views

### 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 ...
2answers
343 views

### Simple MOS current mirror bias circuit

Consider the basic MOS current mirror bias circuitry I am really trying to understand on how Vbias when M3 is 'on' can be any other value other than Vt because M3 is diode connected (Vds= Vgs) and ...
1answer
494 views

### For this current mirror circuit, what is the effect of doubling of the emitter area of transistor Q3?

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 $I_{REF}$.......
1answer
1k views

### Regulated Cascode current mirror

In this regulated cascode current mirror how do we find the minimum voltage across the current mirror? Also, I have read that the current mirror will work even if M1 goes into linear region. But how ...
1answer
2k views

### Wide swing cascode current mirror [duplicate]

This is a high swing cascode current mirror. My question is what is the significance of the connection from the drain of M3 to the gate of M1 and M2? What would happen if both M3 and M1 were diode ...
1answer
817 views

### impedance of basic mosfet current mirror

How to find the impedance looking into the drain of basic mosfet current mirror, including the device capacitances? Is it like the ro of M2 is parallel to Cgd and Cgs. Do we consider the 1/gm from M1 ...
2answers
4k views

### 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?
2answers
2k views

### High Gain Amplifier using BJT

I need some assistance on building a high gain amplifier using only BJTs, capacitors and resistors. I have made some before using op amps, but for this assignment I am not allowed to use Op Amps at ...
1answer
44 views

### Biasing using Current Source

Note: (W/L)ratio of M5 = 3 * (W/L)ratio of M7 I would like to ask if there is a preferable method for accurate current mirroring between the two schematics below. To make it clear what I would like ...
0answers
608 views

### Small Signal Pi Model Current Mirror

The issue I'm having is with Part C. I've rewritten the circuit with the Pi model as such: I can't figure out how to get an iout/i relationship. I can only think of writing the current laws, but it ...
2answers
210 views

### BJT Current source

Why should we use current mirror to make constant current source? Doesn't fixing base current naturally fix the collector current? So why do we use diode connected bjt and then mirror them? Take ...
2answers
253 views

### Current distribution via current mirrors

I tried to distribute a current via pmos and nmos current mirrors (see the schematic below). While the pmos and nmos mirros itself work fine, the distribution from a nmos to a pmos mirror yields an ...
2answers
1k views

### 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 ...
1answer
222 views

### MOS Current Mirror

I was investigating a MOS current mirror on the photo however i could not understand how the equation (3) was obtained from equation (2). I put a question mark also there on the photo. My second ...
0answers
199 views

### Unexpected Output from Widlar Current Source Simulation

I am trying to design a Widlar current source to drive an RC circuit/IC 555 timer. I am having some trouble simulating the current source correctly. I am using LTSpice IV and I am using their 2N2907 ...
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 ...
3answers
475 views

### Why is the current mirrors output unequal?

I made a LTspice simulation of a pmos current mirror. The current source should model a photodiode (without parasitic capacity). The W/L ratio is the same for both Mosfets. I expected the plot of the ...
3answers
2k views

### How to minimize the effect of threshold voltage mismatch of a current mirror?

Consider the current mirror below. As you can see, the circuit is affected by a threshold voltage mismatch, modelled by $V_{mm}$. I want to minimize the effect of the mismatch and dimension the ...
1answer
1k views

### Output Resistance of a High-Swing Cascode Current Mirror

I am wondering how to calculate the output resistance of a High-Swing Cascode Current Mirror from small-signal parameters, see question High-Swing Cascode Current Mirror for the circuit. First I ...
1answer
5k views

### 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 ...
1answer
204 views

### 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 \\$ ...
2answers
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 ...
1answer
276 views

### Current mirror design - gate to drain feedback

In my texbook [Analog VLSI: Circuits and Principles] there are two circuits that function as a current mirror. The first uses two nfets with a shared gate, and the drain of the first nfet (M1) is tied ...
2answers
2k views

### Analysis of the current mirror PNP transistor section

Attached is the circuit I am trying to learn, Lower part with NPN transistors (outside the boxes) are familiar circulatory and and it is self explanatory as well. I am not sure how to is the working ...