# Questions tagged [cascode]

Anything related to cascode amplifier circuits. A cascode (not to be confounded with *cascade*) circuit is a two-stage direct-coupling amplifier topology using two amplifying elements (usually two BJTs or two FETs).

47 questions
79 views

### (Lack of) Miller Effect in Cascode considering Common Emitter and Common Base Seperately

I'm currently working on an analysis of a standard Cascode circuit, in particular why the frequency response is so good as it reduces the miller effect. I have had a very vague explanation given to ...
34 views

### Overdrive Voltage Effect on Cascode Operation

Working on this exercise: I understand that if all the transistors in a cascode have the same current and the same Vgs then they will have the same Vov. However in this case the Vgs do not seem to be ...
65 views

### Telescopic cascode operational amplifier: why not rail the bias nodes?

In a fully differential telescopic cascode opamp, there is a bias voltage for two of the nMOSFETs whose gates are tied together and a bias voltage for two of the pMOSFETs whose gates are tied together....
51 views

### High Voltage Cascode with MOSFET LT Spice Simulation

I'm an electronics engineering student and want to develop a high voltage switch with normal Si N-MOSFETs. After some research, I discovered cascode switches for this application. Most of these ...
55 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 ...
109 views

### Simulation result of bjt cascode amplifier

I use square wave as the input source to my BJT cascode amplifier. However, I got my output voltage as I used transient analysis in PSPICE to obtain the simulation result. Can someone tell me whether ...
35 views

### Maximum mid-band gain of s.s. model MOSFET amplifier?

Schematics I need to find the maximum possible gain for this NMOS cascode circuit. Here is the s.s. model: Work I used nodal-matrix analysis (basis is KCL) to find the gain ($A_v$):  \...
354 views

### Biasing high frequency BJT cascode amplifier

So far, no one in the course has gotten both primary spec: 14.125 (with 1 V/V swing either way) nor 3dB-bandwidth of 500kHz to 20MHz using the 2N4427 (datasheet). Vcc = 9V I_CQ = 10mA-15mA I have ...
63 views

### Midband output voltage of cascode BJT amplifier in PSpice not right

I made a cascode BJT amplifier. $V_{AC}$ = 10e-3 V (ACMAG) From an AC sweep at the output, $R_L$, I need to get a voltage between 200 mV and 250 mV. However, I got 0 V. Why is this so? Do I ...
83 views

### Output voltage in MOS cascode amplifier

I'll give a background to my main question:- In a simple NMOS as shown, while constructing the small signal model of the MOSFET, when there is no resistance between Vdd and drain, NMOS is modeled ...
64 views

### Saturation Cascade MOSFETS (Need Help from EE Experts)

this is a very straightforward question. I'm running a Harmonic simulation on ADS where I need to design a cascode amplifier of two NMOS and one PMOS, that have a gain higher than Av > -100. The ...
55 views

### Setting up a cascode amplifier in a schematic

I had been thinking this for hours. If anyone here could point me if I'm doing the schematic correcly I'd appreciate it. Here's the problem: Consider a cascode amplifier consisting of two stacked ...
155 views

### Importance of Source-Body Connection In MOSFET Cascode Amplifier

While reviewing cascode amplifiers, I found an image on Wikipedia of a MOSFET amplifier, which I reproduced here: The image on Wikipedia has the following caption under the image: Since each ...
62 views

### Folded Cascode Gain

I am designing a single stage folded cascode amplifier. My supply voltage is Vdd=1.2 and tail current= 40uA. I am using gpdk 45nm technology. But in design I have used 200nm as the minimum length. I ...
62 views

### Condition for the output and input impedance for cascading electronic circuits

For cascading a system that have an output impedance of $R_1$ and an op amp that has an input impedance of $R_2$ then in order to use a isolated model we need a value for $R_2$ that is minimal ...
58 views

### Is a cascode better current source than current mirror ? Which option is better?

I have simulated a cascode and made a M2 in saturation so it will act as a current source. I want to understand which current source is better. Is cascode better because it has a higher output ...
180 views

### Vintage Oscilloscope Preamp Whitepaper

Sometime early 90s I came across a whitepaper published by an oscilloscope manufacturer that described a custom preamp IC they had developed for their scopes. Does anyone know of this article? The ...
143 views

### Trying to debug a PWM motor drive with cascode configuration - is the MOSFET busted?

I made a simple DC/universal motor drive as per the circuit in the picture. I was experimenting with it by powering it from a variable transformer. Note that both Vdd (300V) and the 12V Vb1 (for ...
242 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 ...
139 views

### Biasing a cascode in a BJT differential pair

How do I bias the cascode in a differential pair? For some reason when I set it to a constant bias voltage it either does not work at all or the cascode BJTs turn on for only a fraction of the input ...
325 views

### Why cascode transistors contribute little to overall noise in an OTA?

I have read this sentence below in a paper which describes a low noise amplifier. I can't understand the reason why cascode transistors contribute little to overall noise in an OTA?. Can someone ...
795 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 ...
217 views

### Increasing frequency response instead of gain for a Cascode circuit

so this a homework problem that I am working on and I'm not looking for a flat out answer, just a good place to start and some help on the concept. So the question is as follows: Suppose our ...
266 views

### Cascode Amplifier Gain

I've been going through Design of Analog CMOS integrated circuits 2nd Edition by Razavi. I'm currently at the Cascode amplifier section. The author does an example for calculating the gain for the ...
787 views

### MOSFET Cascode: intuitive explanation

How can a MOSFET cascode be explained (not calculated) intuitively? Especiall I would like to know why it's output resistance is high and why the drain voltage of the lower MOSFET M2 is stabilized, i....
478 views

### BJT or Mosfet as Cascode

I was going through this lecture pdf. If I want to have maximum output resistance which cascode configuration I should use. BJT cascode or Mosfet cascode?
368 views

### Increase low-frequency gain of a cascode amplifier

I've been designing a noise generator (for fun) with the goal of getting a smooth frequency response between 10Hz and 10MHz. Since I don't have any "fancy" op-amps, I decided to go with a discrete ...
53 views

### Determining Io/Iref

I'm asked to find the ratio $I_o/I_{ref}$ in the attachment which follows. Normally, due to the current mirror, I'd claim that the ratio should be 1. However, as it's also given in this section that ...
216 views

### Question about common mode feedback

Hi, in the image below (taken from Design of CMOS Analog Design Circuits by Razavi), a high gain amplifier is used to provide common mode sense and feeback by controlling the current through M3 and M4....
731 views

### Current mirror and double cascode

I was asked to determine the input resistance of the circuit in the figure, with and without channel effect. Is there a formula for that which could be applied or must I draw the small signal scheme ...
136 views

### How does resistive feedback affect noise figure?

I am working on a design with cascode CS amplifier with resistors in the feedback. What are the advantages and disadvantages of such topology? How the resistors in the feedback affects noise figure? ...
928 views

### Is the main purpose of cascoding is to increase gain in FETs?

In my recent studies, I have come across the concept of cascoded amplifier using Common Source and Common Gate Configuration. What exactly is the reason of cascoding?
225 views

### Cascode Input Impedance

Please see attached image. I struggling to understand why Rs is negelected in the input impedance; should'nt the total input impedance be the parrallel combination of the capacitor impedance with the ...
301 views

### Output Resistance of this circuit - Cascode

Please see images of question, my working out and the correct solution. I seem to be incorrect for some reason. This is without resorting to the small-signal model.
327 views

### Transient response to rectangular impulse of a cascode common source amplifier

There is a cascode amplifier seen on the picture below. A rectangular pulse with amplitude of 10 mV is sent to the input. Due to large negative amplification gain of the cascode amplifier, output ...
161 views

### single input opamp vs dual input?

Could anyone please refresh my memory regarding op-amps? I am reading this article about Cascodes op-amps to refresh my memory about them - and I see a single input into each op-amp: Is it assumed ...
1k views

### Choosing the bias components of a cascode amplifier

For a two transistor cascode amplifier, how does one determine the base bias resistor ratios? In the design case of a single transistor common emitter, one can use tricks like Ve = Vcc/10 for, from ...
589 views

### Gain equation of cascode common emitter amplifier with an LC tank

I'm trying to find the gain equation of the circuit presented below. I know that for a cascode common emitter amplifier without resistor RE and with a current source instead of the LC tank, the gain ...
361 views

### Cascode Current Mirror 2Vt + 2Von

I've been spending a lot of time trying to know why the gate voltage of M2 is 2Vt + 2Von. I know that if all transistors have the same characteristics then all the Vgs = Vt + Von. Can somebody explain ...
202 views

### Why doesn't my cascode circuit work?

first, i started building a simple circuit in the lab just with one Mosfet and now it is working. then i tried to improve it and add another mosfet as cascode topology.as can be seen in the figure. ...
726 views

The diagram of the cascode was taken from "the Art of electronics": simulate this circuit – Schematic created using CircuitLab The claim is that in this configuration they practically ...
689 views

### PSpice cascode mosfet design not working properly

I'm making a Common Source amplifier using a mosfet and then comparing that to the same basic setup but with 2 mosfets in cascode. However I get a nearly identical response for both circuits. I'm ...
219 views

### Why don't we use cascoding in RF amplifiers?

I need to design an RF amplifier with high gain. It seems every RF book teaches cascading, but not cascoding. Is there a disadvantage to cascoding? It seems like we don't need to match impedances with ...
301 views

### 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 ...
1k views

### Cascoded/Bootstrapped Transimpedance Amplifier

I've come across an interesting transimpedance amplifier toplogy, that reportedly reduces voltage and current noise and compensates for large photodiode capacitance. However, as I'm working with an ...