Hi..
I need an amplifier that it will amplify the 2.5V to 10V..And at output I will put 50ohm resistor to use coaxial cable..
Do have any opinion about it?
Thanks for your replies..
An LM393 may be more common and should be suitable for what you require. There is normaly a filter network on the input for the 40kHz signal. There are many examples on the 'net (or used to be) just try Google.
An operational amplifier uses feedback to control the amount of gain required. The method depends on whether you are using it in inverting or non-inverting mode. Therefore you can set the gain to be anywhere between say, unity to maximum by selecting resistor values.
I would suggest that for this project you search the net for an available design and use that as a basis for creating your own.
It was common to use the 741 for this particular project many years back. It has a gain bandwidth of 1000000 so it works fine, the drawback of course is the need for split rail power supply here.
The problem is that the slew rate limits the full power bandwidth to 8kHz, a 10Vp-p 40kHz sine wave will be distorted to a 1V triangle wave. There's a limit to how fast the output can change, it might be all right for 100mV output at 40kHz but not 10V.
BTW I have used the '358 for parking sensors based on the same idea using 40khz transducers and the unit worked great, again, signal distortion due to slew rate limitation is not an issue here.
The circuit has C3 as a very low value capacitor as compensation for a different faster opamp, not a 741 that has a much higher value capacitor built-in. C3 is not needed with a 741 opamp.
Probably the original opamp worked better with the small value C3 than a 741 at the frequency and gain required. Maybe the original opamp is obsolete so they use a lousy old 741 opamp in that circuit now.
We don't care if the waveshape is triangular. The low slew-rate reduces the amplitude of the output signal because before it ramps to maximum level it is changing its direction.
You guys are correct of course, but it works fine for this application (I designed and sold a few hundred 40khz ultrasonic alarm units in about 1980 using 741's and never had any problems) so I didn't see a problem using it here. I figured the op did not want a 10vpp 40khz output (which is not required in something like this), but rather a 10vdc output when the tranducer was receiving the 40khz signal. Newbies often ask questions in the 'wrong' format so it can be helpful sometimes to try to give them what they need and not what they want.