[RFC] New EEM: Pounder (PDH lock signal generator)

[dtcallcock]

Pound Drever Hall locks are pretty ubiquitous in laser labs. It would be nice to have a Sinara board that does all the necessary modulation and demodulation.

It would sit alongside one of the proposed servo cards such as Stabilizer (Microcontroller Servo) or Fast Kasli Lock.

There are commercial models available from Toptica, Also Toptica, Sacher, Qubig, and Stable Laser Systems. I haven't used most of them but none look like they quite do what we want. At NIST we usually just roll our own from a two-channel standalone DDS, a pile of Minicircuits bits and some custom passive rf filters and a custom active LPF on the output.

Interface could be EEM and/or Ethernet. Having no Ethernet will be obnoxious if we don't want to put an EEM master on Stabilizer. Having ethernet could also make the board on option for people who aren't otherwise using Sinara - the fact there are quite a few commercial products out there demonstrates there is at least some market.

[dtcallcock]

Power detectors we use are : ADL5904 and AD8363ACPZ-WP

Both seem reasonable but the AD8363 goes down to -58dBm whereas the ADL5904 only goes down to -30dBm so I'd probably go for the AD8363.

Attenuators: HMC542BLP4E

Looks good. This part is pretty battle-tested at this point right?

RF switch: HMC349ALP4CE

This switch's power handling totally tanks below 100MHz- we need a switch that can handle what comes out of the power amp. Will have to do a bit of research here.

[hartytp]

1 what’s the use-case for the ext ref? Synchronised locks? If so is it worth having a ref out port? 2 what are the second two dds channels for? 3 is it really worth putting the PA here? Will require some thought about thermal management, biasing (cpu dac?) etc 4 Make the filters dnp by default but allow users to populate as required? Eg the input bpf totally depends on lo freq, the out filter probably needs to be band-stop rather than lpf to maintain phase margin 5 I’d like to make sure the output rf is transformer coupled and can be floated. Ground loops are death for diode current mod 6 fixed gain baseband amp after mixer? 7 expose baseband out on fp as well?

Not sure about 0.5W switch after pa. May need to use (solder?) jumpers

Should we move to a new repo?

[hartytp]

It also has a shutdown pin so it can be connected to the control lines of the switches that switch it in and out of the circuit.

Unless you're starved for IO, I'd put the two switches, amp enable, SMPS enable ? on separate IO so you can ensure proper sequencing. Otherwise preventing races can bit a PITA in these designs.

[dtcallcock]

Just to finish answering @gkasprow questions:

Low pass filter series: LFCN-3000+

Yes, the Minicircuits FV1206 package used in this part should be fine for DDS band defining filters. How about LFCN-160+ (-1.5dB @205MHz, -19dB@300MHz) as the default population?

Fixed attenuators: YAT-12+

MCL YAT series sounds fine.

modulators: ADL5375-05ACPZ-R7, ADL5380ACPZ-R7

I think we just want a double-balanced mixer rather that an AD part. Will open another thread on this.

Low noise generators: CCHD-950-25-100.000, Si570, Si549

See thread on DDS clocking.

[dtcallcock]

what are the second two dds channels for?

For the other PDH channel that's a copy of the first. Reasoning from above:

• It isn't much extra work (just copy and paste the analog section) and will probably add <100 of $ to the board cost.
• Stabilizer is 2-channel
• A lot of atomic references also have an AOM in the pump beam to offset it. You could use one of the two LO outputs for this instead of a second PDH lock. My guess it that this is why Qubig's box has an 'aux LO' output.

[gkasprow]

Here are more-or-less finished schematics. CPU IO assignment is missing. Pounder.PDF