PIN_Diode based radiation particle counter with differential sensing

This is a beta/gamma particle detector designed with differential sensing of the PIN diode signal, to establish some rejection of common-mode EMI. Transimpedance amplifiers with high gain are very similar to an oscilloscope probe amplifier: high impedance and very sensitive to external interference. By sensing symmetrically across both sides of the diodes, common-mode rejection of 40dB can be achieved. In batches of 1% resistor and 5% capacitor tolerances, matching can be achieved of 0.1% for R and 1% for C. This will yield 40dB CMRR.

This design is intended for remote sensing for balloon flights or similar weight-sensitive applications: assembled weight is 3.3g. As such, the added weight (and difficulty) of shielding is avoided, or reduced, by incorporating common-mode rejection.

Notes: For U1 and U3, good opamps are: OPA-2376, AD8692 or TLV2772. U2 is an MCP602. A charge pump voltage doubler is needed to increase the reverse bias across the PIN diodes: this enlarges the diode depletion region, which is where particle detection takes place. The reverse bias makes AC coupling to the opamps necessary.

Do not exceed 5.5V Vcc.

Schematic, gerber files and BOM are on github at the link.

Steve

Note 26 March 2023: There are recommended resistor value changes in the photodiode bias string. R2,3 should be lowered to 4.7 Meg., R1,4 should be lowered to 270K ohm.

Note 3 June 2023: Version 2 of this design, ParticleCounterV2b, is recommended due to performance improvements.