[time-nuts] Si570 question
jimlux at earthlink.net
Tue Nov 18 14:26:06 EST 2014
On 11/18/14, 11:19 AM, Orin Eman wrote:
> I have one of these: http://sdr-kits.net/PA0KLT_Description.html
> built with the CML output Si570 that goes to 1417 MHz (!)
> There is a schematic in the assembly manual that's linked to from that
> page. They use 100n and 1n capacitors in parallel on Vdd and 4K7 pullups
> on SCL/SDA. They have 100n DC blocks directly on the output pins.
> Into a 50 ohm load, the CML outputs produce about 4dBm as I recall.
> Obviously, the CMOS output will be different.
> There is a review of a different Si570 kit on the Clifton Labs site:
> I got similar results comparing my kit against an HP 8640B. The Si570
> beats the 8640B close in just as shown on the Clifton Labs site.
> Some Softrock SDR radios also use the Si570. They use a single 10n
> capacitor on Vdd and 2K2 pullups...:
> I have the Softrock Ensemble RXTX. It works fine on RX, but unfortunately
> I have not been able to get satisfactory image rejection on TX. I suspect
> the FST3253.
> So, it looks like decoupling isn't that critical - 10n or 100n||1n in these
> examples. 1K pullups on SDA/SCL seem to be overkill and anything
> reasonable <= 4K7 should work.
thanks... looks like it's time to stop analyzing and go find a piece of
copper clad to stick this thing down on. I see a lunchtime project
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