opamp, voltage subctration then amplify

[spectrum]

opamp, voltage subtraction then amplify

hello all,

i was looking for an op.amp scheme to subtract and amplify. I'm not asking for a complete circuit. I'm just looking for suggestions, for example what op.amp configuration i have to use, and so on.

As input i have a 125Khz, 200Vpp signal. It can vary sometime from 200 to 199V.

I need to convert this variation into 0-> 1V variation, with a subtracion, then i would like to have the variation amplified as 0-> 5V.

Actually i have available a TLC272 powered 0 and 5 V.

Thanks , angelo

 

[ronsimpson]

We are confused!
You have a 125khz signal that has a voltage of 200 p-p.
It is 200 volts and some times 199 volts.
You want 199 volts to equal 0, and 200 volts to equal 1 volt.
This 0 to 1 volt, is it 125khz AC or do you want DC?
Then you want the 0 to 1 volt amplified to 0 to 5 volts.

Is 5 volts the only low voltage supply around?
Is it OK to go from 199/200 to 0/5 volts direct?
The 0/5 volts is it DC or 125khz AC?
How much current will be pulled from the output?
How accurate 1%, 5%, 10%?
How temperature stable? 1%/degree C?

I need more information! What are you doing?

 

[spectrum]

ok, i try to reformat the question as simple as i can.

I have an information in a 125Khz carrier, 200Vpp. The information is the Vpp that change between 199 and 200Vpp.

Let's cut the signal with a diode, and work only with the pulsed positive part.
If easier to work with pulsed only positive part, after a diode, so 100 and 99,5V are now the levels.

I need to have this information whit a -99,5 offset, a kind of cutting the wave, so i would get 0 and 0,5V information.

I don't have other DC sources thant 0 and 5V.

That's all i need for now.
thanks
angelo

 

[Roff]

ok, i try to reformat the question as simple as i can.

I have an information in a 125Khz carrier, 200Vpp. The information is the Vpp that change between 199 and 200Vpp.

Let's cut the signal with a diode, and work only with the pulsed positive part.
If easier to work with pulsed only positive part, after a diode, so 100 and 99,5V are now the levels.

I need to have this information whit a -99,5 offset, a kind of cutting the wave, so i would get 0 and 0,5V information.

I don't have other DC sources thant 0 and 5V.

That's all i need for now.
thanks
angelo

What does the signal come from? An ultrasonic transducer?

 

[ronsimpson]

To see the difference between 100 and 99.5 is a problem. Electronic parts are not perfect. If I built a subtract 99.5 volt circuit using 5% parts it might subtract 99 volts or 94 or 104.

How many cycles of 125khz are there per bit of information?
One cycle at 99.5 volts =0 and one cycle at 100 volts =1 ?
100 cycles at 99.5 =0 and 100 cycles at 100 = 1?

This makes a big difference on how to do this! The answer could be very complex or simple. I need so see the big picture. E-mail me if you don’t want to tell everyone what you are really doing.

 

[Roff]

To see the difference between 100 and 99.5 is a problem. Electronic parts are not perfect. If I built a subtract 99.5 volt circuit using 5% parts it might subtract 99 volts or 94 or 104.

How many cycles of 125khz are there per bit of information?
One cycle at 99.5 volts =0 and one cycle at 100 volts =1 ?
100 cycles at 99.5 =0 and 100 cycles at 100 = 1?

This makes a big difference on how to do this! The answer could be very complex or simple. I need so see the big picture. E-mail me if you don’t want to tell everyone what you are really doing.

To do it with subtraction, you need a reference 125kHz signal with constant amplitude. Without that, you can use a rectifier, as noted. The reason I asked about the source is it will impact how the rectification is done.

 

[kjennejohn]

Hi.
Is there any reason you can't rectify this through a Schottky diode (0.2V to 0.3V drop) then run it through a two resistor (precision types, 1% or better)voltage divider? Do you need a buffer or instrumentation amplifier, or can you just use a high value (50K - 100K or higher) resistor in the input as a limiter? Of course if you run this through a rectifier bridge you will have a 250KHz signal. If this signal is entirely above the zero point, i.e., all positive, the diode(s) is(are) unnecessary.

Inquiring minds will ask.
'Luck in your project.
kenjj