1. 1 Photovoltaic mode

2. 2 A simple I to U converter Basic building block: I to U converter U = R * I

3. 3 PD bias increases linear range

4. 4 + voltage output buffer... Simple standard circuit. Can be very sensitive, but has generally limited dynamic range.

5. 5 Transimpedance configuration Advantage: larger dynamic range Disadvantage: OpAmp has to take the PD current

6. 6 Transimpedance configuration Noises: R Thermal noise: ~sqrt(R)‏ OP voltage noise: fixed by OP type OP current noise: fixed by OP type, but scales with R Photocurrent shot noise: ~sqrt(I)‏

7. 7 Noise sources as function of R

8. 8 Resonant PD A resonant circuit around the PD (here: C_pd and L1)‏ can increase the dynamic range, depending on the signal content. It can have other advantages, as avoiding non-linearities Z = L1 / (R_pd * C_pd)‏ on resonance Thermal noise according to Z

9. 9 GEO PD circuit

10. 10 New style GEO PD circuit Enhanced dynamic range, multiple resonant outputs

11. 11 LIGO PD circuit variable bias

12. 12 Virgo PD circuit DC current combined to output