Questions tagged [ota]

The operational transconductance amplifier (OTA) is a type of an operational amplifier which differential input voltage produces an output current.

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Implementation of an amplifier in LTSpice

I need to implement the following circuit in LTSpice but I don't know if my schematic is ok. Also, I don't know what values for I should use for Cinf and R2. The following constraints are imposed: ...
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29 views

OTA ca3080 troubles

I having a hard time getting this OTA ca3080 circuit working as expected. It's configured as VCA (or a amplitude modulator. I got the circuit from here: http://www.idea2ic.com/LM13600/UsingOTAs2.pdf I ...
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74 views

Having trouble with OTA CA3080 making a VCA

I'm having trouble getting this CA3080 OTA to work properly. :-( I watched this video ( https://www.youtube.com/watch?v=BbaJ6TOmyVo ) which is quite helpful, but I'm missing a few cues here... In ...
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65 views

Current mirrors inside an OTA (Operational Transconductance Amplifier)

let's consider this transconductance amplifier (OTA) (reference): I have a very basic question. Why do wee need the mirrors M5,M6,M7,M8,M10? Why is the output taken from that current source? Why ...
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47 views

Design of Fully Differential OTA Circuits

This is the equivalent model of an ideal single-ended OTA: Now, this is the equivalent model of an ideal fully differential OTA: Now, is there a rule for getting a certain circuit with a fully ...
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194 views

OTA LTSpice model help

(This is my first post go easy on me) I'm trying to use an OTA to simulate a floating voltage controlled resister like explained here, but I cannot for the life of me figure out how the mota model ...
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28 views

How to control vds drop across each mosfet when several mosfets are stacked on each-other

I am trying to design an folded cascode ota where 4-5 pmos and nmos are stacked on each-other but the problem is there is so much vds drop across one mosfet that the others are not getting the ...
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45 views

OTA with current enhancer

I am working on a "OTA with signal current enhancer". I am using BSIM4 130nm MOSFET model. DC analysis is quite well, but in AC analysis I am getting the response below: Please help me to make this ...
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44 views

Wide Common-Mode Input Range OTA Design

I'm trying to design a 2-stage OTA in a 0.35µm CMOS technology process for one of my analog electronics course projects. I need to design my OTA while following some specs and one of them is common-...
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27 views

How to experimentally calculate transconductance of an OTA?

How can I experimentally calculate the transconductance of an Operational Transconductance Amplifier given that I know the value of bias current ?
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1answer
70 views

How can I find the origin of equation about this filter circuit?

Probably everything is clear for anyone but I can't still understand how can the author found the Vo equation for this circuit. I hope somebody in here will show me the way.
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39 views

What is the Rseen from this node?

In the text book I am reading (CMOS Analog Circuit Design by Razavi) the author wrote that the Rseen from node N is (1/gm7), however when I derived it myself I found that the Rseen is ro4 // ro6 (...
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Definition of operational transconductance amplifier (OTA)

I'm trying to understand the definition of operational transconductance amplifier (OTA). The book on which I'm studying defines it as a class of operational amplifiers which "achieves a high voltage ...
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1answer
104 views

Question about a CMOS operational amplifier

I'm studying CMOS op-amps. At the very beginning of the chapter, the author of my book says: "obtaining low output impedance can be problematic. Nevertheless, the typical use that we make of op-amps ...
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59 views

Why does the frequency of an oscillator changes with the time duration of .TRAN command?

I have simulated an oscillator circuit using OTA in SPICE. It is a self starting oscillator. However, the frequency of oscillation does not change with the bias current but changes with the duration ...
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1answer
217 views

The proper way of using gm/Id plot for designing an amplifier or OTA

For any design of an amplifier or OTA, we are given the specs which we need to achieve including: Gain UGBW or 3db BW Slew rate Power consumption Phase Margin Load capacitance I would like to ...
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1answer
132 views

Simulated inductor for guitar use

Edit: Sorry! Please bear with me, this is my first post! Well, it seems that placing a buffer before certain fuzzes can chance their sound. However, placing an inductor after the buffer cancels this ...
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2answers
4k views

What's the difference between a generated hex file and a binary file in embedded systems?

I have an STM32 project (let's call it blinky). This project is developed using Keil IDE. It blinks an LED every 1 second. When I build it, a HEX file is generated. Let's say I want to upgrade the ...
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3answers
4k views

Understanding Operational Transconductance Amplifiers

I understand the high-level function of OTAs, that they provide an output current proportional to an input voltage. But what I don't understand, and what I can't seem to find any information on online,...
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1answer
192 views

Determining Phase Boost needed to Compensate SMPS

I'm attempting to find the Control-To-Output Bode Plot (open-loop) of a SMPS designed around the TPS54160 so that I can design the type II compensator. The first step in designing a compensator is ...
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112 views

OTA design, the Gm won't go down to zero

I'm trying to simulate a pseudo-differential OTA, but the the Gm vs Vin(differential) plot I obtain seems warped. The Gm won't go down to zero for large values of Vin. attached is the circuit ...
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1answer
600 views

LM13700 Bias Current via Resistor vs. Voltage-Controlled Current Source

I am trying to understand the advantage of using a voltage-controlled current source (VCCS) to drive the bias current inputs of an LM13700 OTA, compared to a simple application of the control voltage (...
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177 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 ...
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1answer
139 views

2nd order high pass filter PSPICE error

I'm working on designing a 2nd order sallen key high pass filter in PSPICE for a school project, but in subthreshold with resistors replaced with OTAs (transamp). Schematics shown in figures below. ...
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1answer
413 views

How to increase the gain of Operational transconductance amplifier by changing the sizes of transistors.

Here is the schematics of the OTA. By changing the length of the transistors I am having more gain but I cannot reach the gain of 200. The maximum gain I reach is 110.35. I want to reach the gain of ...
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2answers
191 views

State Variable Filter - Unexpected High Frequency Behavior

I am designing a voltage-controlled state variable filter for use in a modular synthesizer. Its function is to produce low-pass, band-pass, and high-pass responses for a given audio input signal. ...
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2answers
482 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 ...
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151 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 ...
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698 views

How does this CMOS OTA with common-mode feedback work?

In class I learned about the circuit shown below. It is basically a simple CMOS OTA with a common-mode feedback realized by a resistive divider. But I am not quite sure how it works. Lets say that I ...
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1answer
142 views

Voltage Reference Question

I'm new to regulators and references and I'm trying to update this old circuit that uses an op-amp as a 2.5V voltage reference. The new circuit will possibly use LM4040, but I'm not sure if it needs ...
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3answers
4k views

Intuitive way to see pole/zero directly from schematic

The image below is the electrical configuration and the transfer function of a type II compensator using OTA. By looking at the transfer function, we can easily see that the circuit has two poles (...
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1answer
203 views

How does CMFB works?

I'm working on simple OTA. I know the purpose of CMFB, I just don't know how exactly in this particular case it works: ppt http://s2.ifotos.pl/img/esepng_ahqpseq.png Common mode voltage increases (...
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2answers
279 views

OTA / Common Base (CB) Transistor Circuit

I would like to fully understand the following schematic. Especially the nonlinearities are of interest. (Supply Voltage is +/-15V for both OpAmp and OTA) It's an amplification circuit and the in ...
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1answer
471 views

Do it yourself operational transconductance amp?

While quickly prototyping some of diy-synth circuits I realized that I don't have OTA at hand, but I wanted to continue fiddling with the circuit. Is there a way to make OTA out of op-amps and ...
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434 views

an LM13700 can be configured as a “floating” voltage controlled resistor ; How resistor-like is it?

I want to use an LM13700 as a voltage controlled resistor, and I want it to act like a rheostat. When will it act non-linearly? The description of this circuit is on page 15 of the datasheet, and ...
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1answer
872 views

Help understanding frequency calculation for VCO Schematic in LM13700 Datasheet

I am trying to work through the math of the following schematic pulled from the LM13700 datasheet: I can certainly hook this up and mess with the values to change the frequency range to my liking (...
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998 views

Voltage Controlled Butterworth Hi-Pass Filter using a Transconductance Op Amp?

In the Texas Instruments datasheets for the LM13700 Transconductance Op Amp (as well as the earlier National Semiconductor versions) there's been an application note showing a voltage-controlled 2 ...
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1answer
2k views

How to use a current source with current control pin of LM13700

I am trying to bias the lm13700 Input amplitude bias current pin with a current source rather than using a voltage source and current limiting resistor as shown in all the data sheet schematics, but ...
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1answer
702 views

Is it permissible to use fractional aspect ratio W/L for MOSFETs?

I am designing a 2-stage op-amp (Miller compensated). For compensation, I am using a nulling resistance R in series with the compensation capacitance C, with the resistance implemented using a ...
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1answer
2k views

LM13700 Control voltage?

I'm trying to build the circuit shown below. This is a VCA, application taken from Nuts & Volts magazine I think (don't have the article). I know very little about OTAs in general but from what I ...