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Using LMV1012 preamp to amplify signal from a JFET EMC

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Replies: 4

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Hi,

I'm working on application to amplify the signal on a 2-wire JFET based EMC. The application intend to allocate the preamp close to the EMC instead of placing on the processing board to avoid amplifying both signal and noise. Is the LMV1012 a good selection for such application, in this case parallel the LMV1012 with EMC internal JFET.

Thanks,

Kwan

4 Replies

  • Hi, Kwan,

    My concern would be too much gain in your system. The LMV1012 is designed to be connected directly to mic capsules without integrated amplification.

    -d2

    Best regards,

    Don Dapkus

    Gate Driver Applications

    Dallas, TX USA

     

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  • Hello Kwan-san,

    LMV1012 will be not good selection for your application because as Don-san mentioned LMV1012 connects to MIc diaphragm directly and JFET will have 0 to couple d of Gain. I'll recommend you to take LMV1032 to connect EMC with JFET. Please take look at LMV1032 dtasheet pg 9 Fig-6 which is showing how to connect with external EMC with LMV1032. LMV1032 has gain option for 6dB, 15dB and 25dB. you will select your prefered gain option.

    Best regards

    T NAOKAWA

  • In reply to Toyojiro Naokawa:

    Hi Naokawa san, Thanks for your recommendation. The LMV1032 requires external Vdd. We plan to put the amp close to EMC which only have 2 wire, output and gnd. Is there a solution to it? If using LMV1032, we'll have to put on the PCB at the end of 2 wire, but that will amplify both the signal and noise. Thanks, Kwan
  • In reply to Kwan:

    Hello Kwan-san,

    Your EMC has JFET interally. It means that the capacitive transducer is connenected between Gate and Source of JFET. The drain of JFET is EMC output. To work this JFET correctly, you will put RL (around 2K Ohms) via about 2V or higher.it will be depending on IDSS on JFET. LMV1012 works looks like just replacement of this JFET but has much gain.  If you want to put LMV1012 close to EMC and interface to LMV1012, you still need RL and supply to give proper bias to JFET. If you take LMV1012 instead of JFET, then you can connect 2 wire at the end but need RL and supply at the end.  But JFET output and LMV1012 output will be very similar which means both cases required RL and supply at the end the output is DC bias current + output current then to have voltage output, you need to put RL externally . So your EMC with JFET will be OK to use as it is. because the output style of LMV1012 is the similar to JFET. Only different is the gain. at the end point. JFET will be about 0dB or so. If you are warried about Rf noise on output line, you will put cap between output and GND at close to EMC output.

    Best regards

    T NAOKAWA

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