Need Amplifier

[cGr]

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..

 

[blueroomelectronics]

How much current?

 

[cGr]

I am not sure now,but ı will use it with ultrasonic sensors..

 

[cGr]

The current is about 0.5 mA..It's gain should be 4..For exp. 2.5V should be 10V...
Thanks for your replies..

 

[Gordz]

What sort of frequency are you looking at here ? This will affect the gain etc. If it is up to 40kHz you will probably get away with LM358 or so...

 

[cGr]

It will be 40kHZ..
Is LM358 suitable?Or is there any commen amplifiers..

 

[Gordz]

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.

 

[cGr]

Thanks..I want to ask this in datasheets;
Voltage Gain GV --- VCC =15V, RL≥15KΩ
(for large VO(P-P)swing) 25 100 - V/mV

What does it mean?Can ı adjustment the gain to 4??

 

[Gordz]

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.

 

[cGr]

I solved my problem with using 741..Thanks for your helps..

 

[stevag]

Well then, cGr, show the circuit and performance.

 

[Hero999]

I'd be surprised if it works, the 741 is barely good for audio, let alone ultrasound.

 

[Gordz]

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.

 

[Hero999]

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.

 

[audioguru]

An LM358 is even slower than a 741 opamp.
With a 40kHz sine-wave input its max output is a 3V p-p triangle-wave.

 

[Gordz]

Here is an example using a 741 - UaShem.com | Security and other sensors and detectors | UltraSonic Radar
For doppler shift use the fact that the waveform is more triangular is not a problem. The signal is normaly squared up or amplified to clipping point anyway.

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.

 

[audioguru]

Here is an example using a 741

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.

 

[Hero999]

It isn't a radar, it's a sonar because a radar uses radio and a sonar uses ultrasound.

 

[audioguru]

The very simple sonar motion detector does not use doppler shift. It simply detects a change in the amplitude of its ultrasonic reflection.

 

[Gordz]

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.