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Electronics

One Inch Photodetector, v1

Here's a transimpedance amplifier board that fits inside a 1" lens-mount. It has low noise LDOs (LT3042 and LT3094) and a SOT-23-6 op-amp footprint (for e.g. OPA657 or OPA847).

The first board has a S5973 photodiode, an OPA657, a 10 kOhm feedback resistor, and a 0.2pF feedback capacitor. The circuit self-oscillates without any feedback capacitor.

The backside of the board has an MMCX-connector for the output signal, and 3 wires for power supplies (max +/-20V).

The noise-floor shows an ~18 dB bump as the 59 MHz -3dB bandwidth is approached - not that great. At low frequencies the noise-floor agrees with the thermal noise of a 10k resistor. Shot-noise from about 10uW optical power, producing a 4 uA photocurrent (photodiode responsivity ~0.4A/W), should be clearly (3 dB or so) above the 10k resistor thermal noise floor.

The noise-bump could be decreased with a larger feedback-capacitor, but this reduces bandwidth. The source capacitance is due to the S5973 photodiode (1.6 pF) and the differential (0.7 pF) and common-mode (4.5 pF) input-capacitance of the OPA657 op-amp. Clearly a lower input-capacitance opamp would be better. Stay tuned for tests with OPA858...

Note to self: can't use the Siglent SA's default detector mode of "Positive-peak" if we want quantitative dBm numbers from the analyzer. Use "sample" detector mode!

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OPA858, OPA855, OPA859

High-speed op-amps from TI, in a somewhat challenging WSON8-package...

OPA858 is a 5.5 GHz GBWP FET-input amplifier (stable at gains >= 7V/V), and the OPA859 looks like a slower 1.8 GHz unity-gain stable version.

OPA855 is a 8 GHz bipolar input opamp, gain >=7V/V.

These should be useful where OPA847 and OPA659 were used previously, e.g. in high-speed transimpedance amplifiers.

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SO-20 Texas PowerPAD

SO-20 PowerPAD footprint as used by e.g. OPA569

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LTC1562

LTC1562 quad op-amp for building active filters at 10 kHz to 150 kHz.

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Electronics

Pulse distribution amplifier rise-time measurement

With a longish BNC-cable between a PDA-output and a 4 GHz oscilloscope we see a 10%-to-90% rise-time of <700 ps.

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Electronics

Multiplexer S/N 4

Slight design changes to the RF Multiplexer design.

Front panel buttons B1 and B2 now extend out of the front-panel and are easily accessible. Pressing the buttons advances the state of the MUX1 and MUX2 boards.

Transmission bandwidth. This MUX has 50-Ohm impedance relays, and the 3dB bandwidth is around 1.0-1.2 GHz.
Inside of MUX-box. Two 1:8 boards with BNC connectors side-by-side. Arduino MKRZERO and Ethernet Shield on the right. A simple carrier board distributes SPI-signals from the Arduino to the MUX-boards and provides front-panel pushbuttons and LEDs. Top center is a 230VAC to 5VDC powersupply. Top left 230VAC input.

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LT3045

500mA low-noise voltage regulator LT3045 (in contrast to the older but lower current 200mA LT3042)

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BUF602

1 GHz buffer amplifier BUF602.

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LT3042

low noise voltage regulator LT3042

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SFP connector footprint

Single SFP/SFP+ SMD-connector and cage footprint.