Electronics – anderswallin.net

Crystek CVCO55 VCO

Cliff horizontal 4mm shrouded Banana connector

Amphenol vertical BNC connector

Bourns PTV09A-1 potentiometer footprint fix

This footprint had too small mounting holes, and the potentiometer-shaft in the wrong place. https://gitlab.com/kicad/libraries/kicad-footprints/-/merge_requests/2991

250MHz detector with Fermionics FD80FC photodiode

Here's anoter one-inch-photodetector with a Fermionics FD80FC photodiode and 5k1 transimpedance. Bandwidth around 250 MHz. Predicted dark noise and frequency response with TIASim. The Fermionics diode has a capacitance of only 0.4 pF (80 um diameter active area), giving slightly better bandwidth than a Thorlabs FGA01FC (2 pF capacitance, 120 um diameter active area).

Measured frequency response, compared to TIASim prediction

120 MHz FGA01FC/OPA818 photodetector with 12 kOhm RF

PCB: One Inch Photodetector

Transimpedance model: TIASim

Previous similar designs:

200 MHz photodetector (RF 4k7)
400 MHz photodetector (RF 1k2)

New SMA-to-SFP breakout boards

I made a new batch of the SFP Breakout Board.

With a 1 Gbit/s SFP transciever the bandwidth when transmitting from the TX port of one board to the RX port of another board seems to be almost 1.8 GHz.

200MHz photodetector with OPA818, FGA01FC InGaAs photodiode, and RF=4k7

Here's another one-inch-photodetector using OPA818 with a 2pF@5V InGaAs fiber-coupled photodiode FGA01FC. With a transimpedance gain of 4k7 Ohms the bandwidth is just over 200 MHz. A TIASim model predicts the dark-noise and response reasonably well with a parasitic capacitance (over RF) adjusted to ca 0.12 pF. The spectrum-analyzer settings weren't ideal for looking at the dark-noise which should go down to the thermal-noise of the 4k7 resistor (dashed line) - but here the instrument noise-floor prevents us from seeing that.

SFP-board in a box

Update: first production batch being tested in the lab 2020-12-17:

By popular demand, I've worked with Aivon to put my simple 'SFP2SMA' board (https://github.com/aewallin/SFP2SMA_2018.03) in a box, using an external Meanwell (+12V, -12V, +5V) PSU with a 5-pin DIN8 plug (model GP25A13D-R1B, Digikey 1866-1826-ND). The board can be used for simple frequency-transfer experiments together with almost any SFP-transciever. The TX SMA-connector is an input, and applies the waveform to the TX-pins of the SPF, producing modulated optical output. The dual RX SMA-connectors are driven by the SFP RX-pins, with some gain applied to produce around +10 dBm square-wave into a 50R load.

The front panel has three SFP status-LEDs: TX-fault (I've never seen this, but apparently the SFP should report if the TX-laser fails), RX LOS (loss of signal, active if you unplug the fiber), and mod_abs (module absent, active if no SFP is plugged)

After some adjustments to gains and component values the frequency-response is flat within 3 dB out to ca 400 MHz, and the ADEV looks reasonable at ca 1e-13/tau(s) (red datapoints in the plot below). These measurements were done with a CWDM SFP and a 2m single-mode loopback-fiber.

The box is a Hammond 1455L1201 (120 mm x 103 mm x 31 mm), with custom front and back panels.

Front panel with TX, SFP, and dual RX outputs

400+ MHz photodetector with OPA818

One-Inch-Photodetecor in Thorlabs 1" mount. LT3093 negative-rail voltage regulator at the top, and LT3042 positive rail voltage regulator bottom right. OPA818 op-amp bottom center, with BUF602 output-driver bottom left.

After a number of failed attempts (with HMC799, OPA859), here is a reasonably fast One Inch Photodetector using OPA818, a FDS015 photodiode, and 1.2 kOhm transimpedance. Bandwidth is above 400 MHz, with the dark-noise and frequency-response in reasonable agreement with TIASim predictions.

With the detector blocked there's quite a lot of electrical feed-through with just the spectrum-analyzer TG-output on (see blue data points, especially above 1 GHz). I tried to correct for this roughly, shown as the orange data points.