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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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How to test the stability of an OTA in this case?

I am designing an OTA for a current buffer (images from Analog Design Essentials): The OTA is just used to provide a high gain, to regulate the voltage on RE. My question is, how to test the ...
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Transconductance and voltage gain of LT1534

In the datasheet of the LT1534 it says the error amplifier transconductance is 1.5 mS (typ.) and the error amplifier voltage gain is 250 V/V (typ.): But on page 11 it says the output impedance of the ...
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How to calculate this close loop gain for this OTA circuit?

Try to find close loop gain of the following is the circuit (\$\gamma = 0\$, body effect can be omitted). $$Q_1 = Q_2, Q_3 =Q_4$$ Here is what I have tried to solve. We have to break the loop and ...
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Voltage gain of differential amp with active load (OTA)

In solving the differential pair with an active load and parasite resistance R1 is included, I am stuck on how to proceed. This was a question from Razavi's Design of analog CMOS integrated circuit, ...
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UART software flow control in ESP32S3 and OTA using cellular modem

I'm using an ESP32S3 chip and trying to implement OTA through a cellular modem. The size of the bin file is 1250KB. The cellular modem has an AT command that downloads all the content in one go. Since ...
cyber122010's user avatar
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Minimum compensation capacitance for 45 degree phase margin in two-stage CMOS OTA

I'm working through a solved example problem on compensation of a two-stage op amp. For extra context, this example problem is originally from an exam of a now-concluded course offering, so it is ...
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2 votes
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Clamp transistors in folded cascode for slew rate improvement

Razavi's textbook Design of Analog CMOS Integrated Circuits (2nd edition) includes a possible option of improving the slew rate of a folded-cascode amplifier in Figure 9.77, included below (along with ...
Halleff's user avatar
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Difference OTA and op-amp

I have a question about OTA (operational transconductance amplifier). Why can an OTA can be used without negative feedback but would still be able to keep its inputs (V+, V-) close each other? I have ...
AnalogMan's user avatar
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STM32 - update firmware from data stored in SRAM

I would like to remotely update the firmware of my STM32WLE5 device. I can transfer the new binary file from the server to the STM's SRAM using my custom link only, which means I cannot utilize other ...
Foreen's user avatar
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What affects the unity-gain bandwidth (UGB) of a symmetrical OTA?

I am trying to determine the sizing of transistors in the OTA as shown below. A strange thing I found earlier was that a small output impedance of M5 would cause a much smaller GBW than designed, as ...
Jack Black's user avatar
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How does Vds affect the overall transconductance of this OTA?

I am trying to determine the sizing of transistors in the OTA as shown below, using the gm/id methodology. I wanted gm1 and gm2 to have much larger gm than the other transistors to reduce noise. I ...
Jack Black's user avatar
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How to define the input common-mode voltage in this circuit?

I am trying to simulate the circuit below (from this paper) at the transistor level using a 0.18um, 1.8V process. The circuit serves as an amplifier for recording neural activities, and uses 2 ...
Jack Black's user avatar
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145 views

LTspice OTA simulation does not work

I am trying to simulate a balanced OTA with TSMC 350 nm technology in LTspice. Here is the TSMC 350 nm library for LTspice. I designed the balanced OTA topology below: Thd output current is almost ...
anilberg's user avatar
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Why does PFC often use OTA to do the compensation?

I see some design documents about PFC, they often use OTA to compensate for the circuit. I know the OPA is voltage control voltage and OTA is voltage control current, but I don't know why I can't use ...
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5T OTA Vout in Cadence simulation is always just VDD?

I'm working on an 5T OTA with the following schematic: Here's the simulation circuit: I'm using a VDD = 2.5V since the transistors are rated for that in the model library I'm using. My issue is that ...
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Voltage-controlled amplifier output offset

I'm testing a voltage controlled amplifier circuit in a simulator. The circuit is powered by a single 9V supply, so a "virtual ground" equal to 1/2 VCC is used. I have a question about the ...
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LM13700 does not completely reduce the sound

I have a problem with LM13700 - it does not completely reduce the sound when the control current is zero. For testing, I put together the most basic circuit, where the control pin is connected to the ...
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Is there anything wrong with using large values for L/W for a PMOS?

Worked on a project recently for a linear circuit design course. Professor gave us the requirements to build a 5T OTA circuit which must have a gain of 30dB, unity frequency of 200kHz, etc. Designed ...
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Voltage controlled amplifier with single supply

I'm trying to make a voltage controlled amplifier circuit to control the feedback level of a delay effect. My big problem is that the circuit must be powered by a single power supply. I seem to have ...
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Discerning slew rate and bandwidth limitations

What I get is that, considering a 2 stage OTA, we have 2 effects that limit the amplitude and frequency of the amplified signal: Bandwidth of the amplifier: as the frequency of the input signal gets ...
concerned middle age man's user avatar
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How can a voltage multiplier be used as variable resistance?

I am interested in voltage control and variable resistance and I have tried with OTA, vactrol, and diode. I read that a voltage multiplier (DC to DC?) can be used for this purpose. Is this multiplier ...
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Differential pair with active load including resistance

In solving the differential pair with an active load, I am able to find the gain without including R1 as shown in the figure. When R1 is included, I am stuck on how to proceed. Could you help me out? ...
prashanth's user avatar
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Transfer function of OTA based neural signal amplifier

I was reading about OTA based neural signal amplifiers and reached this schematic Based on the book's description the transfer function for this circuit design is : but unfortunately couldn't find ...
Pooya Estakhri's user avatar
1 vote
1 answer
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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?
Microelec's user avatar
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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 ...
Chris_26's user avatar
10 votes
1 answer
2k views

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 ...
Granger Obliviate's user avatar
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1 answer
460 views

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 ...
Scipio's user avatar
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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), ...
meekeech's user avatar
2 votes
1 answer
367 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 ...
NaturalDemon's user avatar
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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 ...
寅子敬's user avatar
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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 ...
meekeech's user avatar
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106 views

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 ...
NaturalDemon's user avatar
2 votes
0 answers
170 views

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 ...
apoch's user avatar
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1 answer
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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,...
Uroc327's user avatar
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1 answer
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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 ...
floating_resistor's user avatar
3 votes
1 answer
444 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 ...
RAN's user avatar
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2 answers
384 views

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 ...
Underdog's user avatar
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1 vote
2 answers
342 views

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 ...
Jonathan Donald's user avatar
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2 answers
156 views

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 ...
xampierre's user avatar
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1 answer
112 views

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=...
bicanul123's user avatar
0 votes
4 answers
455 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: ...
bicanul123's user avatar
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1 answer
305 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 ...
user3810130's user avatar
1 vote
1 answer
814 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 ...
user3810130's user avatar
0 votes
1 answer
951 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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2 votes
1 answer
446 views

Design of fully differential OTA circuits

This is the equivalent model of an ideal single-ended OTA: This is the equivalent model of an ideal fully differential OTA: Is there a rule for getting a certain circuit with a fully differential ...
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1 answer
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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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1 answer
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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 ...
Owaller's user avatar
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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 ?
Anirban Choudhury's user avatar
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1 answer
72 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.
ömer koçhan's user avatar
2 votes
1 answer
361 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 ...
Stefanino's user avatar
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