[hpsdr] Power supply filtering

[J.D. Bakker]

Hi all,

I hadn't seen this paper mentioned yet:

http://www.linear.com/pc/downloadDocument.do?id=4159

In this document, Linear Technology's Application Note 70, a 
switchmode power supply design is presented with less than 100uV 
output noise, and little RFI. This is achieved by using a switch 
controller which has controlled output switch slewing, allowing a 
trade-off between EMI/RFI and efficiency. Methods to measure and 
control PSU noise are also discussed (IMHO, the EMI sniffer probe in 
Section J is particularly interesting).

The document is mostly about the LT1533; two other chips worth 
mentioning are the LT1683 and the LT1738 which implement the same 
slew control with an external FET, enabling designs with higher 
output power.

>Perhaps we should make sure that Demeter has
>the ability to phase-lock it's switching
>frequencies to Gibraltar; possibly with offsets.

That definitely helps, especially if the ADC sample clock can be 
similarly locked & shifted.

BTW: contrary to popular belief, linear PSUs are NOT inherently 
noise-free. The cap charging current spikes through the rectifier 
diodes can produce plenty of EMI/RFI.

JDB.
[not associated with LT in any way other than having used these chips 
in very low noise portable digital audio recorders]
-- 
LART. 250 MIPS under one Watt. Free hardware design files.
http://www.lartmaker.nl/

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