Photodiode transimpedance amplifier, on a one inch diameter (25 mm) circular 2-sided PCB - for mounting in a standard 1" lens-mount.
TIASim can be used to predict gain, noise, and bandwidth using different op-amps, transimpedance-gains, etc. Initial results show that capacitive loading on the MMCX connector, when connecting a coaxial cable to Spectrum Analyzer or Oscilloscope, plays a role. For un-buffered op-amps TIASim predictions agree with measurements when op-amp GBWP is 'de-rated' slightly - probably due to the capacitive load on the output. Latest PCB versions use a buffer/cable-driver BUF602 to isolate the sensitive transimpedance amplifier from output loading.
The board features low-noise LDOs LT3042 and LT3093 to produce +V and -V DC-rails for the op-amp. The photodiode footprint is TO-18, to fit e.g. Hamamatsu Si photodiodes S5973, S5972, S5973, or Thorlabs Si detectors FDS015, FDS025, FD11A, or Thorlabs InGaAs detectors such as FGA01, FGA01FC, FGA015, FDGA05, FD05D, FD10D.
Thorlabs photodiodes seem to match OSI part numbers:
- Thorlabs FGA01FC, marked INGAAS-120L-FC
- Thorlabs FDS015, marked FCI-125G-006HR
- Thorlabs FDS025, marked FCI-125G-010HRL
Photodiodes with alternative pinout (OPA818alt PCB, 2.54mm pin-circle-diameter, 1 Anode, 2 Cathode, 3 Case):
- Fermionics FD80FC, InGaAs, 0.4 pF capacitance
- Hamamatsu G9801-32, InGaAs, 1 pF
The output is DC-coupled to a MMCX connector, to fit the small board.
Examples of completed and teseted boards:
- (OPA818alt-board, BUF602 output buffer) OPA818, Fermionics FD80FC, 5.1 kOhm RF 250 MHz bandwidth.
- (OPA818-board, BUF602 output buffer) OPA818 op-amp, FGA01FC photodiode, 4.7 kOhm RF, >200 MHz -3dB bandwidth.
- (OPA818-board, BUF602 output buffer) OPA818 op-amp, FDS015 or FDS025 photodiode, 1.2 kOhm RF, >400 MHz -3dB bandwidth.
- (SOT23-board, unbuffered) OPA657 op-amp, S5973 photodiode, 10 kOhm RF, around 59 MHz -3 dB bandwidth. With measured signal and noise spectra
- (SOT23-board, unbuffered) OPA657, S5971 photodiode, 1 MOhm transimpedace, 4 MHz bandwidth
(May 2020) SOT23 detector mounted in 1" lens-mount. DC-inputs (+,GND,-) at the bottom. LDOs left and right of the DC-inputs. Photodiode center. Op-amp at the top with MMCX output-connector on the backside of the board, top right.
This is the best performing board so far, in terms of bandwidth!
NOTE: the prototype-board has not worked correctly so far. shows self-oscillations. build at your own risk!
HMC799 is a 10 kOhm transimpedance amplifier with up to 700 MHz bandwidth.
This design also uses a BUF602 output buffer, to hopefully avoid capacitive loading of the transimpedance amplifier as coaxial cables are connected to the output.
This version of the detector is for a SOT23 op-amp such as OPA657(FET 1.6GHz), OPA847(bipolar 3.9GHz), and similar.
This version is for modern op-amps in WSON8 footprint such as OPA855(bipolar 8GHz), OPA858(FET 5.5GHz), OPA859(FET 1.9GHz)
