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HMC799 Photodiode Pre-amp

I wish to use the HMC799 on a photodiode pre-amp. Is it possible to dispense with the 22nF RFin capacitor and connect the photodiode anode to pin 3 of the HMC799 and the cathode of my APD to the detector bias voltage of say +60V. The TIA will then create a -ve voltage excursion internally but without knowing the details of the circuitry inside the device I do not know if I will get a correct -ve excursion at the output pin 10. 

Any advice?     

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  • Hi,

    DC coupling of HMC799 and APD is doable, yet you have to make sure that the dark current or ambient induced current is not saturating the dynamic range of the HMC799.

    Best Regards

    Sinan

  • Hi Sinan,

    I am currently using the HMC799 with a PIN PD. But, since I also need the DC output, I am operating it without the 22nF capacitors at PIN 3 and PIN 10. Moreover, the current from the PD is in the microamps range (so does not saturate the TIA). When I biased the HMC at 4.5V and checked the output using an oscilloscope, it shows a DC output of ~1.8V though there is no input signal from the PD. I had designed a custom PCB just similar to the one indicated on the datasheet (124020-1), but without the J1 connector (since the photodiode is connected to the HMC directly on the PCB) and the 22nF capacitors at the RF IN and RF OUT ports. Additionally, the bypass capacitors in my PCB are larger than those mentioned on the datasheet (I assume that is not a problem). Moreover, the current meter from the biasing power supply indicates 100mA instead of 70-90 mA as mentioned on the datasheet. Do you think it is normal? And, where does the DC output come from? Also, I measured the same voltage as the output (1.8V) at the RF IN pin and across the 22nF capacitor at the CEXT pin. The voltage (at the output port and the input and CEXT ports) increased steadily from 0V to ~1.8V when I increased the bias voltage from 0V to 4.5V. Is this normal? I Looking forward to your quick reply. Thanks.

    Regards,

    Ketema

Reply
  • Hi Sinan,

    I am currently using the HMC799 with a PIN PD. But, since I also need the DC output, I am operating it without the 22nF capacitors at PIN 3 and PIN 10. Moreover, the current from the PD is in the microamps range (so does not saturate the TIA). When I biased the HMC at 4.5V and checked the output using an oscilloscope, it shows a DC output of ~1.8V though there is no input signal from the PD. I had designed a custom PCB just similar to the one indicated on the datasheet (124020-1), but without the J1 connector (since the photodiode is connected to the HMC directly on the PCB) and the 22nF capacitors at the RF IN and RF OUT ports. Additionally, the bypass capacitors in my PCB are larger than those mentioned on the datasheet (I assume that is not a problem). Moreover, the current meter from the biasing power supply indicates 100mA instead of 70-90 mA as mentioned on the datasheet. Do you think it is normal? And, where does the DC output come from? Also, I measured the same voltage as the output (1.8V) at the RF IN pin and across the 22nF capacitor at the CEXT pin. The voltage (at the output port and the input and CEXT ports) increased steadily from 0V to ~1.8V when I increased the bias voltage from 0V to 4.5V. Is this normal? I Looking forward to your quick reply. Thanks.

    Regards,

    Ketema

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