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'[EE]:Voltage Amplifier'
2001\01\21@113829 by Erwin Stevanus

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Hi all,
I want to use an amplifier for my ultrasonic receiver. the output of my
ultrasonic receiver is very small (few mV) at 40 kHz that i want to amplify
the signal to around 2-5 Volts. I have tried using simple design of
operational amplifier, the inverting and non-inverting op-amp, but i could
not get the output.

Anybody can help??


Erwin
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2001\01\21@122640 by Oliver Broad

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I think if you want to use low cost opamps you will have to cascade them.
Otherwise I think you will need an opamp with an extraordinary
gain-bandwidth figure (the frequency in the opamp data table) something
close to 400MHz!

Also what supplies are you using, if you run the amp from PIC VCC and GND
you will need biasing to make the signal sit between the supplies.

Oliver.

{Original Message removed}

2001\01\21@125208 by Dan Michaels

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At 05:33 PM 1/21/01 -0000, you wrote:
>I think if you want to use low cost opamps you will have to cascade them.
>Otherwise I think you will need an opamp with an extraordinary
>gain-bandwidth figure (the frequency in the opamp data table) something
>close to 400MHz!
>

Yes, for typical opamp with 1mhz GBW [LM358, LM324], max gain usable
at 40khz is only about 1Mhz/40khz = 25, and you probably need gain
>1000.

Might try LF353/TL082-84, with 4mhz GBW --> gain=100. Also, make
sure all cascaded stages are AC-coupled, including gnd leg gain
resistor, if single-ended supply being used:


                  |  \opamp
----.1uF---+------|+  \
           |      |    +----+------.1uF-- (repeat 2x or 3x)
          100K  +-|-  /     |
           |    | |  /      |
           |    |           |
          gnd   +----100K---+
                |
               1K
                |
              .1uF
                |
               gnd

Use another 100K resistor from "+" input to +Vcc, for single-ended
supply.

Lastly, play around a lot with ckt values.

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2001\01\21@155703 by Olin Lathrop

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> I want to use an amplifier for my ultrasonic receiver. the output of my
> ultrasonic receiver is very small (few mV) at 40 kHz that i want to
amplify
> the signal to around 2-5 Volts. I have tried using simple design of
> operational amplifier, the inverting and non-inverting op-amp, but i could
> not get the output.

So you want a gain of about 1000 starting at a few millivolts with around
100KHz bandwidth.  By the way, a few mV is not very small.  It is well large
enough to allow such amplification without introducing much noise.
Microphones often put out in the microvolts range.

A gain of 1000 if a bit much for a single stage.  I would use two stages
each with a gain around 30.  That means you need amps with gain*bandwidth of
somewhat over 3M, which isn't that hard to find.  Two stages also allows for
high pass filtering between the stages to eliminate DC offsets from the
first stage.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olinspamKILLspamembedinc.com, http://www.embedinc.com

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2001\01\22@151355 by Peter L. Peres

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imho use a tuned amplifier (using a tank coil meant for tape erase
oscillators). This is the 'easy' way. If you are trying to do sonar then
you will need to implement an ultrasonic preamplifier with wide band
filters.

Peter

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