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Transimpedance Amplifier. Ultralow Noise JFET  Buffers the Current Noise of the Bipolar LTC6406 Input  Trim the Pot for 0V Differential Output under No-Light  Conditions.

This circuit shows the LTC6406 connected as a single-ended transimpedance amplifier with 20kΩ of transimpedance gain. The BF862 JFET buffers the LTC6406 input, drastically reducing the effects of its bipolar input transistor current noise. The VGS of the JFET is now included as an offset, but this is typically 0.6V so the circuit still functions well on a 3V single supply and the offset can be dialed out with the 10k potentiometer. The time domain response is shown in Figure 4. Total output noise on 20MHz bandwidth measurements shows 0.8mVRMS on VOUT+ and 1.1mVRMS on VOUT–. Taken differentially, the transimpedance gain is 40kΩ.

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