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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Derive open-loop frequency response from close-loop characteristic

How can I derive open-loop frequency response from close-loop characteristic of a real Operational transconductance amplifier?
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OTA via BLE on Cypress CYBLE-222014-01 Module

I have developed an application using the CYBLE-222014-01 module which acquires a set of data and transmits it over BLE. Now I would like to add OTA functionality to this project, however the ...
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Analog Design of a Miller OTA: Am I doing it right?

So I am doing a class on analog design. I have to design a two-stage Miller-compensated OTA. I would like to have some feedback about my design procedure and also some help because I am stuck. My ...
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Finding the gain expression for this CMOS operational transconductance amplifier

So here's the circuit: I think M2 is a common source amplifier and M4 a common gate amplifier, so they form a cascode amplifier where the gain is given by : Av = -gm2 * r0, r0 is the impedance at the ...
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How do I bias two OTAs without dividing the current?

I'm trying to achieve automatic gain control in an audio circuit, which requires me to use both diode pins of each amplifier available on the LM13700 chip. The diode pins accept a current (Idiode), ...
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125 views

Is there a simple fix for summing 2 AC signals?

I have seen many mixer schematics. They are pretty much always the same - a stack of resistors. Even some DJ mixers using the SSM2164 simply joined outputs followed by an opamp. The same thing always ...
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Is Razavi wrong? ---- Two-state op for Bandgap

The picture comes from the paper "The Design of a Low-Voltage Bandgap Reference", IEEE SOLID-STATE CIRCUITS MAGAZINE SUMMER 2021. I think the output of the first state should be the drain of ...
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Why is my voltage pulsing when using a DAC as an input to an OTA?

I'm using the LM13700 in an automatic gain control configuration to adjust the volume of a speaker based on the audio level perceived by the microphone. Both amplifiers on the chip are used: one to ...
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how to shut of the buffer of a BA6110 OTA?

What would the best way to shut off a BA6110 OTA buffer? Tie pin 7 high (+15V) Tie pin 7 low (-15V) Tie pin 8 buffer out back into pin 7 (which I believe is wrong, I tried that before and might have ...
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2 votes
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LM13700 Gain Calculation

I pulled some LM13700 OTAs from an old board and tested them. All voltages, currents, and resistances were measured. I had the expected (approximate) voltage gain using the equation \$ A=(R_2/(R_1+R_2 ...
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Functionality of output stage of a cmos amplifier circuit

I have the following circuit and I'm wondering a little bit about the functionality of the output transistors M12-M19. simulate this circuit – Schematic created using CircuitLab I know that M1,...
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I'm having issues setting up the LM13700 as a floating resistor and measuring the correct resistance values

So I'm still learning how OTA's work, and have an application using the LM13700 as a floating voltage controlled resistor as seen below: I'm using +/-12V rails for this circuit. I have it set up so ...
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2 votes
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230 views

Complex conjugate poles for OTA unity gain

So I am designing an OTA, exactly like Miller OTA, but I tried to see the behaviour without Miller compensation. The circuit diagram is shown below As seen there is no compensation network, neither ...
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Why can the drain of a transistor be used as an output port in both OTA and TIA?

In OTA, the output is current. It should deliver a constant current to the next stage. So the output impedance of an OTA should be high. As the impedance seen at the drain is also high, it is ...
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LM13700 control current appearing as voltage at output?

I've got an LM13700 in this VCA configuration, and for whatever reason the gain control input (I'm applying a triangle LFO, ranging from 2-7v) is appearing as a voltage at the output. Does anybody ...
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How to understand signal inversion and current flow through OTA?

In the following example schematic for an OTA, transistor M4 is said to be non-inverting input while M3 is the inverting input. The given explanations are short and i find them rather unclear. M4 is ...
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Can't compute the value of Resistance of Operational Transconductance Amplifier [duplicate]

I have the following Operational Transconductance Amplifier that I need to implement in LTSpice. I need to choose a value for \$R_2\$ and \$C_{inf}\$ in order to have a (theoretical)gain value \$A_v=...
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4 answers
280 views

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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1 answer
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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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1 vote
1 answer
385 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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362 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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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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Simulation of an Operational Transconductance Amplifier in Orcad Capture

I wanted to simulate an OTA (Operational Transconductance Amplifier) by using a block G representing a controlled source (I have also put input and output resistances): First question: how can I ...
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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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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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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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2 votes
1 answer
197 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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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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1 vote
1 answer
626 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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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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8 votes
2 answers
10k 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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4 votes
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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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1 vote
1 answer
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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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1 answer
160 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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8 votes
3 answers
8k views

Floating voltage-controlled resistor with LM13700: How does it work?

1. The LM13700 The LM13700 is an Operational Transconductance Amplifier (https://en.wikipedia.org/wiki/Operational_transconductance_amplifier) converting a differential voltage into a current output. ...
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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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1 answer
239 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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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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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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2 votes
2 answers
316 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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3 votes
2 answers
623 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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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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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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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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3 answers
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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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3 votes
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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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2 votes
1 answer
608 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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2 answers
2k views

How can I simulate in PSpice the model LM13700?

Hello to everyone and apologies if this question has been asked before, but I am searching more than an hour every time before I post. I want to simulate the LM13700 Operational Transconductance ...
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1 vote
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511 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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1 answer
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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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