Any low power low frequency quadrature receivers?

[John S]

First we'd have to mix it down for that because my signal will be at
5-10MHz carrier frequency. Can also be undersampled, of course, but
that'll cost a little SNR. Which would probably be ok in this
application, we don't need to be able to hear the grass grow.

Initially I thought about using a PSoC because it already has digital
blocks for the quadrature oscillator generation. Also switched-capacitor
blocks which I should be able to "mis-use" as mixers, and then opamps
for some gain. But I am not a programmer whizkid. Once we get into a
higher volume project I'll revisit that, possibly a PSoC-3 is the ticket
here if I disable the uC in there. The on-board ADC capabilities are a
bit paltry though.

Paltry? I think it's a 20-bit ADC.

 

[Joerg]

Paltry? I think it's a 20-bit ADC.

Yes, but AFAIR if you need any reasonable speed like tens of KSPS it'll
drop to much less.

 

[John S]

Yes, but AFAIR if you need any reasonable speed like tens of KSPS it'll
drop to much less.

True. 20 bits at up to 187 SPS, 16 bits at up to 48k SPS, 12 bits at up
to 192k SPS.

I know that's not the best, but for an on-board I thought it pretty good.

 

[Joerg]

True. 20 bits at up to 187 SPS, 16 bits at up to 48k SPS, 12 bits at up
to 192k SPS.

I know that's not the best, but for an on-board I thought it pretty good.

If it was 16bits up to 192kbps I'd be really happy

 

[John S]

If it was 16bits up to 192kbps I'd be really happy

Ok, so now I know your definition of paltry ADCs.

 

[Nico Coesel]

Why not use a cheap microcontroller, low current like the Cortex M0
NXP series.

Simple analog bandpass filter of the incoming signal, syncronize a ADC
from a PWM Local Osc generated by the micro, use a low frequency FIR
filter to regenerate the shifted down signal from the undersampled
output of the ADC.

The ADC needs to be triggered with low jitter, but that should be
simple.

The Cortex M0 can run at full speed below 1mA, add another 1mA for a
1MSa/s ADC. A number of other microcontrollers can do the same, the
Cortex is just a very nice part.

Sounds like a nice idea. IIRC the ADC on NXP ARM devices can be
triggered by a pin as well.

 

[[email protected]]

If such silly patents haven't run out all it takes is proof that you
dunnit 25 years ago and ... poof ... blows it out the water.

That and a megabuck or two.

 

[Allan Herriman]

Come to think of it, I've done this using CMOS switches as the "mixer"

I've done that using CMOS switches as well, about 19 or 20 years ago.
455kHz with a 74HC4053 running from +/- 5V. I had a ring counter made
from 74HC74 flip flops to make the quadrature switching signals for the
'4053.
This was the last IF in a 30GHz tracking receiver.

Regards,
Allan

 

[Joerg]

That and a megabuck or two.

Depends on how compelling your evidence is. I've so far never had to go
to the mat on any legal stuff. The (very) few times it came to a head
there the guys looked at the evidence and decided to bury the hatchets.

 

[Joerg]

CMOS switches make pretty good mixers. Good MOSFET mixers have a higher
IP3 than just about anything--I still miss the late lamented Si8602.

If you ever come across the absolute cat's meouw for any sort of analog
chip get a tube of them. That's what I did with the mother of all
mixers, the Plessey SL6440. Just in time before it all went under. Same
with the LH0063 and LH0033, because they never made anything even
remotely comparable and I kind of knew they wouldn't.

 

[[email protected]]

Simple analog bandpass filter of the incoming signal, syncronize a ADC froma PWM Local Osc generated by the micro, use a low frequency FIR filter to regenerate the shifted down signal from the undersampled output of the ADC.http://www.hqew.net/product-data/74HC4052