Buffer from a CURRENT FEEDBACK AMPLIFIER

[nikhilsigma]

hey guys....

I want to make a voltage buffer... i.e. a unity gain amplifier from a CURRENT FEEDBACK AMPLIFIER.....(https://www.ti.com/product/ths3202)

Please help....

 

[FvM]

Voltage buffer (G = +1 amplifier) is just a special case of the non-inverting amplifier discussed in the datasheet. You'll also find the suggested Rf value for G = +1 and performance curves.

More detailed circuit schematics can be found in other CFB OP datasheets like THS3001 or THS3201.

 

[nikhilsigma]

thanks for helping.....can u please tell me how to make a peak detector with this opamp (for detecting sin wave peak)....

 

[crutschow]

What is the maximum frequency and minumum voltage of the sine wave?

 

[FvM]

At first sight, I doubt that a CFB OP ist partcularly suited to build a peak detector. It can be used for the buffer stage, but the diode stage can be better driven by VFB OP.

 

[nikhilsigma]

Sine wave is 4Vpp with a frequency of 1MHz.....

I have LM7171(220MHz) and this CFB Opamp(2GHz)....

so what should I use to make a peak detector ???
and please suggest me a circuit that can work at 1MHz...

 

[crutschow]

How do you want to reset the circuit for another reading after it detects the peak voltage? Do you just want an RC decay with some time constant or do you want a triggered switch to discharge the peak storage cap?

 

[FvM]

LM7171 is compensated for minimum gain of +2. A standard feedback peak detector circuit relies on a unity gain compensated amplifier.

 

[nikhilsigma]

anything will work....

my aim is to detect the amplitude of incoming sin wave....
and after taking reading with uC's ADC, sin wave will be turned off.....so the output of peak detector can delay by itself or by an external switch....
there will be atleast a gap of 2seconds between two readings.....so it can decay within this period...

 

[FvM]

In my view, a peak detector isn't the first choice to measure a sine wave amplitude, because it's more sensitive to noise and signal distortions.

 

[nikhilsigma]

okay....I need to measure the amplitude of sine wave....so what should I do ???
please help

- - - Updated - - -

frequency of operation will always be 1MHz....and maximum voltage level of 2Vpeak( i.e. 4Vpeak to peak)....

 

[crutschow]

You could use a precision rectifier. Look at page 19 of this AD8037 spec sheet for a precision rectifier that operates to 20MHz. For 1MHz operation you can increase the value of the feedback resistors for a higher input impedance if you like.

You can then run the output through an RC low-pass filter to give the average value of the sine-wave.

 

[nikhilsigma]

crutschow Thanks alot for helping....

I have two questions...

1. that configuration uses VL PIN which is not present in LM7171 opamp.....so how can I design a full wave or half wave rectifier of 1MHz with 7171 ??
2. are diode based precision rectifiers not good for high frequency signals ??

 

[FvM]

are diode based precision rectifiers not good for high frequency signals ??

Unless you refer to special hardware like AD8037 clamp amplifier, you'll use a classical precision rectifier circuit, I guess. They have of course some limitations.

Your reference to precision rectifiers suggests a counter question.
Did you already try to implement a precision rectifier for your application in simulation or real hardware? What are the results?