Multistage Amplifiers offset and gain

I am not so familiar with Opamps, but I would like to combine the following circuits with each other. and would greatly appreciate the help I can get in designing this. I have red some theories about opamps, books like opamps for everyone, simulated with Qucs and I aint getting the results I expected using the program, I tried configurations with Differential and selfbuild Operational amplifiers but to no avail, you are probably familiar with this.

Information

What I do know is that the input and the output are connected to a 50 Ohm BNC cable.

0.15V TTL input unipolar and like to amplify it towards maximum 5V with an Potentiometer, and should have a variable offset also connected with a potentiometer.

Configuration(required)

AC to DC Adapter 12V 400mA

LTC3265 Voltage Pump for stable 15±V

Low pass filter 6 order, gain, offset, voltage follower.

5x TLV074 for the opamps

Questions:

is the configuration in correct order? filter, gain, offset, voltage follower?
I havent found that much on google about this.

what do I need to keep in mind? as in where to start with, and the steps to follow?

is there a general rule for configurations like this?

(I included a drawing of how it should look like, the Gain and the offset should go to the back, due to noise amplification of the signal.)

sincerely yours

Bastiaan

I'm pretty good with op-amps, but I'm not an active filter expert.

0.15V TTL input unipolar and like to amplify it towards maximum 5V

Well... TTL is digital and it's nominally 0V low and 5V high. So, you don't normally amplify it linearly.

So, what kind of signal is this and what's with the filtering?

And, what are you trying to do with the offset? Are you simply trying to adjust-out any op-amp offset error, or are you trying to add or subtract offset from the signal?

Most everyday op-amps can't drive a 50 Ohm load, but they can drive a 50 Ohm cable at relatively low frequencies (because the cable is only 50 Ohms at radio frequencies).

Gain first, using a low-noise precision device if possible, and this is then the only part of the circuit
susceptible to interference and needing to be precision. But to be honest you can easily do gain
and filtering in one stage, or offset and gain in one stage, so you don't need 4 stages, 3 or even 2
could be done.

I presume these BNC leads are 50 ohm terminated, or there's not much point using them? That
would mandate a high current buffer output stage.

Some details of the bandwidth, specifications of the filter, offset adjustment range, accuracy
requirements etc would be nice

Is a TLV074 a TL074? Either way its not a single-supply opamp, its not suitable with just that 12V
supply. You'd need +/-12V rails or +/-15V rails, which is a real bore these days.

The AD8656 dual 5V rail-to-rail opamp is about the best opamp I've found thats low noise,
fast, precise and rail-to-rail. It only works upto 5V supply, but its capable of +/-75mA output
if you don't mind it only reaching 0.5V from each rail (output stage is about 7 ohms, basically).

Your first stage is shown without any feedback.

In this condition it will have an extremely high gain, and is likely to saturate from any noise on the input.

You need to include negative feedback to control the gain of that stage.

Hi,
What is the application?
What do you want the circuit to do?
What is the input signal and what do you expect to get out?
The drawing title says amplifying TTL signal.
If all you are doing is changing the height of a TTL square waveform, there are easier ways than this.

Tom...... :slight_smile: