deepika97

Hi,

I am working with a feedback circuit for a sensor. I excite the sensor with a sinesodal voltage of aroung 50-200mV and 1K-500KHz. The output of this sensor is to read and so it is amplified. Now I need to put back the output voltage to 50-200mV since it is a feedback. I tried to use an AGC for this purpose but turned out to be real complicated for low amplitude signals. So I thought of using an diode clamping circuit to serve my purpose. But this gives a square wave of different harmonics. I need to convert this to a sine wave to avoid this. Can you suggest me any circuitry to serve my purpose. Can you also suggest any simple circuitry for AGC if any. Kindly do this help.

Regards,
Deepika

ronsimpson

I have a hard time understanding.

What sensor type? Data sheet?
Please send more information.

deepika97

the sensor which i am working is a micro device which is a piezoelectric cantilever. I do not have any datasheet for this because it is fabricated by ourselves in our lab. I need to excite this device using the piezoelectric material with the help of a signal generator. I hope I am clear about this. If you do not understand let me know so that I can try to help you understand better.

Cheers,
Deepika

ronsimpson

Does the sensor have only two pins or does it have ‘input’, ‘output’ and ground pins?

What is the output voltage from the sensor? What gain range do you need for the AGC?

I think no one has answers for you so I will ask questions until we understand better.

ron s

deepika97

The sensor has two pins. one input and one output. The output of the sensor usually ranges from microvolts to millivolts. So I feed the output to an current difference amplifier where I can read the signal in volts(2-3V). I also read its frequency. This is a moisture sensor. So when it is exposed to the atmosphere it senses moisture which results in a change in its frequency. Now I feed this signal back to the input but the amplitude should be really low in the range of 10mv-200mv because higher voltages result in its breakdown ( the sensing part of this device is far thinner than one strand of the hair). So I have tried using AGC in order to control the output amplitude of the amplifier to mV but that is really complicated as I can see a lot of noise in my circuit. So can you suggest me any simple circuitry which can serve my purpose. The other way to control this amplitude is to use a diode clamping circuit. But this generates a square wave and I cannot use this square wave to excite my device because it results in odd harmonics and I have to take a really good care of the frequency. So I am thinking of using a square to sine wave converter so that I can use the sinesoidal signal of amplitude 10-200mV to excite my device through the feedback. Hope I am clear this time. But if you have any questions further let me know.

Regards,
Deepika