Ryan
Joined: 22 Feb 2006
Posts: 2
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 Posted:
Wed Feb 22, 2006 6:45 pm Post subject:
Low-noise highpass (0.01Hz) circuit with response to 10MHz |
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We are making high-dynamic range amplitude noise measurements of lasers (offset frequencies from near DC to >10MHz). To get the large dynamic range, we run average photodiode currents up to 10mA. Currently, we use a transimpedance amplifier with <6nV/√Hz output noise, OPA643, Rf=330ohm followed by a very large blocking cap (2000uF, fc=1Hz in 50ohm system) and then DC-40MHz, (50ohm input) low noise amplifiers (>40dB gain). However, we want to investigate close-in noise (down to 0.01Hz), we must block DC (up to 4VDC) to avoid saturation of subsequent amplifiers. Therefore, we need a low-noise highpass filter with fc <0.01Hz, and a passband to at least 100kHz, preferably >10MHz.
Suggestions for low noise circuit topologies?
Best Regards,
--Ryan
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