This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

interfacing of op-amp with ASK transmitter

Other Parts Discussed in Thread: TLV2371

 I am trying to interface the amplified data of the op-amp TLV2371 to the ASK(amplitude shift keying) transmitter (working at 433MHz) but as soon as ASK transmitter is coming in  the functioning, it is blocking then output signal of the op-amp and a constant data is being seen on the oscilloscope. Could this be the problem of the matching between op-amp or ASK transmitter?  I am not able to understand this problem?

regards

Akhilesh Sati

  • Akhilesh,

    It seems that you may be getting some RF interference affecting the op amp. Can you please provide a circuit diagram and details on the application? With this information such as data rate, waveforms, etc. we may be able to recommend circuit changes or different op amp types that will improve performance.

    Regards, Bruce.

  • Thank you sir for your response.

                                                Actually the application is to amplify the received square waveform(digital signal) across the combination of a reverse bias LED and 1k resistor (the circuit is shown below), here the current of the reverse bias LED is modulated by through the light which is originated from the serial port of the MSP430 at the baud rate of 1200 bps. Actually, when the transmitter is either directly connected with the serial port of the MSP430 OR tested with the square waveform Upto 5 KHz generated from the function generator, it is also working fine.

    I think there may be some problem with the output stage of the op-amp TLV2371, which I am not able to understand.

    regards

    Akhilesh

  • Akhilesh,

    If I understand correctly, the circuit only malfunctions when the 433MHz transmitter is activated. Is that correct?

    The second op amp is used as a comparator and will probably be less sensitive to RF. The problem is more likely occurring in U1. You have not described the physical layout of this circuitry. It should be kept as compact as possible. All connections, especially on the input circuitry from the LED to U1, should be kept as short as possible. These connections will act as an antenna.

    Rectification of RF may occur in the LED or input circuit of U1 that may disturb the circuit. Move the RF transmitter as far as possible from this sensitive circuitry. Try adding a 1nF capacitor at the non-inverting input of U1 to ground (very short leads).

    You should have a good bypass capacitor on the 3.3V supply pin of U1--short leads, located close to U1.

    Monitor the output behavior of U1 with and without the RF transmitter operating to see the difference in the behavior.

    These issues can be very difficult for us to troubleshoot without our "hands on" your circuitry. With some patient troubleshooting and experimentation, you should be able to make significant improvements.

    Regards, Bruce.

  • I agree with your points but I don,t think that this kind of problem would occur due to noise because the amount of noise,entering through the LED , U1 and due to their interconnection would be filtered by the comparator stage(U2) itself  & we would be getting a clean digital signal. The problem is as soon as the ASK module is getting activated it is just clamping the output of the op-amp at a 3V constant signal, which otherwise should have been a square waveform of 1200 bps.

    Sir, I think the problem could be due to the output stage of the op-amp TLV2371, I will have to try it with a different Single supply op-amp!

    regards

    Akhilesh