This box is to replace the BNC AA box in the ATF as well as the Sander Liu AA PEM chassis in the 40m.
- Use same box as the ATF BNC AA or something better. No need for awesome flame spray.
- 2 stage, switchable whitening
- whitening stages selectable by front panel 3 state toggle
- Box Inputs are floating BNC (panel mounted / not board mount)
- Whitening input is fully differential
Input noise < 10 nV/rHz (for what frequencies ???)
High impedance inputs (> 100 kOhms)
- Input range of +/ 10 V (i.e. 10 V will rail the ADC).
- AA output are differential to the ADC
- Box output has SCSI connection with appropriate strain relieving lugs on the panel.
- Board can be removed from box fairly easily.
- Whitening is customizable by the user. Each opamp/stage is a second-order active filter.
- All opamps to be chosen to have a minimum slew rate of 10 V/us.
- +/- 15 V for powering internal opamps. Power via the low-noise power modules. On/Off switch on the back. Indicator lights on front and back. NO GREEN LIGHTS.
- The ADCs will be clocked to sample at 65536 Hz, so the AA should cut off everything above 32 kHz and notch out 65536 Hz.
Front End
The input of the box needs to be high impedance, low noise, gain =1, and have a high CMRR. There are no commercial opamps which meet all 3 specs and so we roll our own using opamps. Nice guide for making 3 opamp instrumentation amps. InstAmpDesignGuide.pdf
We probably want to use this kind of thing for the AA input. The commercially available Inst-Amps all have a lousy noise performance unless they're used with a gain of >10. Since we want to put a gain of 10 into the demod boards, this is not acceptable. We want the minimum gain between the RF Mixer (LSC) and the ADC to be 10. So the DC gain of the Whitening/AA must be 1 or 2.
Switches / Relays
For the switchable whitening should we use electromechanical relays or (SSR) solid-state relays?
We want that the switching only require ~5V and less than 100 mA to switch. Also the on-resistance should be less than 10 Ohms.
The S134D-5 or S134D-6 from Teledyne seems like a good choice for electromechanical relay.
We often use the MAX333A as a SSR. This is also used in the Sigg MC/CM circuits.
What is the right switch?
Design Notes
RFI Filter on Inst Amp front end: Needs to remove f > 20 kHz w/o unbalancing lines. Nice guide on p 5-12 of the Analog Devices InstAmp Guide. The input RC filter for the differential input has an R = 100 Ohms and a C = 47 nF so as to have XXX of attenuation at NNN Hz and less than NNN deg of phase shift at NNN Hz.
- Choose the right switch for the filters - should not be a relay. Fix the footprint.
Altium / PCB Design
Working Notes
- Need to make front panel design
- AD8004AR-14 should be swapped out for ADA4004-4
- Doublecheck performance of MAX4158. OK for noise? On-resistance? footprint?
Are these OK? http://www.wima.de/EN/tpl_products_smd_overview.htm
Calculate and label actual R & C values.
- WIMA caps are sold by Mouser. MKP-4 are good ones.
- FP LED: green, (SSI-LXH312GD12V150)
- ask Chub about back panel, what size, what box? also get LN power circuit, power switch, power connector, indicators for back panel.
- add small bypass caps on each opamp