Design notes
Draft notes during design phase
Existing 3U boards
- CTDAB has been originally designed for pulse transmission, but has already been tested in operation with the GMT 500KHz DC-balanced signal.
- CTDPR has been originally designed for pulse reception, but we confirmed in simulations and in the lab on the existing 3U boards that it can achieve reception of a DC-balanced signal up to >10MHz
Optical components selection
- Regarding the transmitter, note that we need high power bandwidth (around 1mW) due to the expected high attenuation and the sensitivity of the receiver
- The HFBR-2316T receiver has been successfully used in CTDPR since years. According to the company Broadcom
> _"There are currently no foreseen plans to obsolete HFBR-1312TZ nor
HFBR-2316TZ.
> The above transmitter/receiver combination is designed for
signal/data transmission over graded index multimode fibers e.g. 50 or
62.5/125µm.
> Only the receiver can also be used with single mode fibers.
> The transmitter is a 1300nm LED with optical power coupled in
multimode fiber between about 10-100µW.
> A 1mW version is currently not available."_
Receiver HFBR-1312TZ input optical power
In the Electrical/Optical and Dynamic Characteristics of the
HFBR-1312TZ we
see
On our setup with CTDAB and CTDPR we noticed that when the optical power
at the receiver CTDPR was ~500uW (CTDAB, without attenuation), the
signal in the output was ~16ns longer.
The following pictures zoom in a rising and a falling edge of a 5MHz
signal (200ns pulse width) at the input of the CTDAB transmitter
(yellow) and at the output of the CTDPR receiver (pink).
The rising edges with or without attenuation show ~40 ns skew.
The falling edges with attenuation (that means optical power at the
receiver ~10uW) show also ~40 ns skew, as the rising ones.
The falling edges without attenuation show 40+16ns= ~56 ns skew, as we
are exceeding the Peak Input Optical
Power.
CTDAB-CTDPR system latency
In the setup we connected the CTDAB to the CTDPR with just few meters of
fiber.
We measure in yellow the GMT input of the CTDAB and in pink the output
of the CTDPR.
The system latency as the following figure shows is is
~36us.
Files
- opt_repeat_measur.xlsx
- CTDPR_LTspice.asc
- rx_peak_input_opt_pwr.png
- rising_-20db.JPG
- rising_no_atten.JPG
- falling_-20db.JPG
- falling_no_atten.JPG
- GMT_latency.jpg
- GMT_latency.jpg
- CONV-RS485-OPT-RTM-RX_sim.asc
- Preseries-testsetup.png
- Preseries-testsetup1.png
- Preseries-testsetup1-oscillo.png
- Preseries-testsetup2.png
- Preseries-testsetup2-oscillo.png
- Preseries-testsetup2.png
- Preseries-testsetup1.png
- Preseries-testsetup2.png