EMRFD Message Archive 11171
Message Date From Subject 11171 2015-06-12 13:26:21 wb9kzy Quadrature LO from 2x clock input: LT5517 PE1KTH mentioned using the LT5517 - after looking at the spec sheet I noticed the 2x clock input. They don't elaborate on how this is accomplished but it appears to be deriving a digital level 2x clock (and inverse) from the 2x LO input - those clocks then drive 2 flip flops to generate the LO.
Is it that simple ?
There appear to be many ham quadrature mixer designs which use a 4x clock.
11172 2015-06-12 13:35:36 Tayloe, Dan (Noki... Re: Quadrature LO from 2x clock input: LT5517
2x clock can be used to generate quadrature clocks if the 2x clock has very close to 50% duty cycle. Some folks have used this approach in the past.
- Dan, N7VE
11173 2015-06-12 15:12:51 Dave Re: Quadrature LO from 2x clock input: LT5517 It is that simple. All of the 4X designs use the first stage to generate 2 outputs 180 deg. out of phase. Many drivers as well as the non-CMOS Si570 already produce complementary outputs. In my UHFSDR I use the complementary outputs from the Si570 and 2 flip flops to produce I and Q at 1/2 the Si570 frequency.
Dave - WB6DHW
11174 2015-06-13 04:23:28 jorschei Re: Quadrature LO from 2x clock input: LT5517
The builders manual is available on the site from PA0RWE describing the use of the LT5517 mixer from LINEAR.
Be aware thad the specification from LINEAR go down to 40 MHz bud there is somewhere a note from LINEAR thad also ISM can be used with the LT5517 thad is 13 MHz. We use further down to 3 MHz and found 7 MHz was always working. "bud to go down to 3 MHz" depend on the factory production number Batch run, "production spreading".
We had to select Batch numbers to find the the 3 MHz useful LT5517 items. This a nice mixer and there is a Italian Ham using the KTH-SDR kit for EME receiving with good results.
I think thad the Si570 2xF generator can be replaced with the Si5351A for HF receiving even if the Jitter is worse compared to the Si570. Jitter is not so dammatching as we taught for HF ,listen to the sounds files in the PE1KTH Files with Dan Tayloe his sampler front + Si5351A on MW 1008 KHz AM and on a noisy 80 meter SSB. And the current is lower aprox 25 mA. The PCB set's only are still available.73"Joris PE1KTH
11175 2015-06-13 05:15:16 DuWayne Schmidlko... Re: Quadrature LO from 2x clock input: LT5517 Check Analog Devices app note " AN-1100 Wireless Transmitter IQ Balance and Sideband Suppression".
About half way down there is a circuit for generating quadrature signals from a 2x LO, just a clocked D-FlipFlop and an inverter.
11176 2015-06-13 06:35:58 jorschei Re: Quadrature LO from 2x clock input: LT5517
Read the data sheet of the LT5517 the VFO in is 1:2 is in the LT5517 chip.
VFO is 2 x RX
11177 2015-06-13 09:52:31 Dave Re: Quadrature LO from 2x clock input: LT5517 The inverter in the 2nd clock line will introduce a skew due to its propagation time. Better to use an exclusive or gate (74AC86) in each clock line. The 2nd input of the 1st gate is tied to + and the 2nd input of the 2nd gate is tied to ground. That will reduce the skew to the difference in the propagation time of the 2 exclusive or gates. If they are on the same die, that time will be very small.
Dave - WB6DHW
11185 2015-06-14 05:34:52 wb9kzy Re: Quadrature LO from 2x clock input: LT5517 Dave -
Thanks for the clever idea - if I do the arithmetic right, 1 degree of skew at 7 MHz is about 400 picoseconds !
11186 2015-06-14 05:54:29 wb9kzy Re: Quadrature LO from 2x clock input: LT5517 Joris -
Thank you for all the info/links.
11187 2015-06-14 05:56:14 wb9kzy Re: Quadrature LO from 2x clock input: LT5517 DuWayne -
Thanks for the link to the app note.
11188 2015-06-14 06:01:03 wb9kzy Re: Quadrature LO from 2x clock input: LT5517 Dan -
I can see that going from a 2x to a 4x clock is adding one more IC and having to use a higher frequency VFO. Which is probably worth it if the skew problems are reduced.
11189 2015-06-14 07:32:32 Paul Cvanaugh Re: Quadrature LO from 2x clock input: LT5517 Sent from my Verizon Wireless 4G LTE DROID