[time-nuts] Buffer / distribution amplifier for TCXO
bruce.griffiths at xtra.co.nz
Wed Aug 4 22:42:41 UTC 2010
The GPS receiver chip actually specifies that a clipped sinewave should
Presumably this is necessary to limit the harmonic contents.
In which case low pass filtering the CMOS outputs may be necessary.
The 74AHC04 or equivalent may be a better choice as its ground and Vcc
bounce is lower than that of a 74AC04.
Bob Camp wrote:
> I suspect you will find that the phase noise floor of the distribution
> system does indeed matter.
> Likely the "easy way" to go:
> Square the TCXO up with a biased CMOS inverter (at least as fast as a
> 74AC04). Run a seperate inverter to drive each of the receivers. A hex
> inverter chip would do it all quite nicely. There should be plenty of
> isolation and far more signal than is needed. Attenuating it at the
> receiver with a pair of resistors should get all the levels to match
> up. If you want to get fancy, transformer couple into each receiver
> after attenuating.
> From: "Henry Hallam" <henry at pericynthion.org>
> Sent: Wednesday, August 04, 2010 1:46 PM
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Subject: [time-nuts] Buffer / distribution amplifier for TCXO
>> Dear time nuts,
>> I have built a GPS receiver based around the SE4120L front end IC .
>> I used a KT3225 TCXO  at 16.3676MHz driving the front end through
>> a 10nF series capacitor as in the example circuit in . Inside the
>> front end, this oscillator is multiplied up to form a local oscillator
>> at 1571.2896 MHz. The 16.3676MHz signal is also divided to form a
>> 4.0919MHz sampling clock. Digital I and Q samples then go to a DSP
>> where the GPS signal processing is done in software. My receiver
>> works nicely, getting it online was a boatload of fun and I'm hoping
>> to make it available soon along with open-source software as a GPS
>> experimenter's kit.
>> I'd like to clock multiple receivers from a single 16.3676MHz
>> oscillator, in order to combine measurements from multiple antennas.
>> The clocks must be at the same frequency, i.e. from the same source,
>> but it is not necessary that they have any particular phase
>> relationship as phase offsets are removed in the navigation
>> What sort of distribution amplifier should I use to split the output
>> of one TCXO into four front ends? Do I need some kind of impedance
>> matching network? How would I go about designing that? This sort of
>> analog/RF design is unfamiliar territory for me, though I'd like to
>> The TCXO advertises a minimum output level of 0.8Vpp into (10kohm in
>> parallel with 10pF). The front end requires a minimum oscillator
>> drive level of 0.2Vpp. The front end datasheet lists "recommended
>> crystal parameters" including a load capacitance of 10pF (typ),
>> although I don't know whether or not that refers to the front end
>> input capacitance.
>> My guess is that phase noise performance is not particularly crucial,
>> at least by time-nuts standards. I guess it would be nice if the
>> amplifier didn't make the phase noise "significantly" worse than it
>> already is from the cheap TCXO.
>> Many thanks,
>> Henry Hallam
>>  http://global.kyocera.com/prdct/electro/pdf/tcxo/172_e.pdf
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> and follow the instructions there.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> and follow the instructions there.
More information about the time-nuts