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 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.
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