Download H.Grote - Photodetector circuits

Photovoltaic mode
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A simple I to U converter
Basic building block: I to U converter
U=R*I
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PD bias increases linear range
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+ voltage output buffer...
Simple standard circuit.
Can be very sensitive, but has generally
limited dynamic range.
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Transimpedance configuration
Advantage: larger dynamic range
Disadvantage: OpAmp has to take the PD current
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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)
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Noise sources as function of R
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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
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GEO PD circuit
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New style GEO PD circuit
Enhanced dynamic range,
multiple resonant outputs
10
LIGO PD circuit
variable bias
11
Virgo PD circuit
DC current combined to output
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