Author Topic: Looking for programmable clock generator IC, 1 Hz - 20 MHz  (Read 832 times)

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Offline andybrandiTopic starter

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Looking for programmable clock generator IC, 1 Hz - 20 MHz
« on: August 27, 2020, 10:33:53 pm »
Hi! I'm looking for an IC to generate a clock signal for a DAC application (a personal project) that can be programmed to output arbitrary frequencies from roughly 1 Hz to 20 MHz. There is room for variation in the minimum frequency, but I need to get reasonably close to DC, and all of the affordable clock generator chips that I could find so far start at >1 kHz.

Further requirements:

- ideally no/few external components (although an input/reference clock signal is available, if needed)
- hand-solderable, bonus if DIP package
- programmable via SPI/I2C or similar
- reasonably low-cost (say < US$2)
- widely available in single quantities

Remarks:

- a single output channel is sufficient
- no constraints on output or supply voltage levels


Any suggestions? Admittedly, I could probably find one myself if I only searched for long enough, but if there's an obvious choice, I'd be happy to be enlightened.  :D Thanks!
 

Offline MasterT

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Re: Looking for programmable clock generator IC, 1 Hz - 20 MHz
« Reply #1 on: August 27, 2020, 11:42:08 pm »
In this price range only Si5351 comes to mind,
https://www.arrow.com/en/products/si5351a-b06208-gt/silicon-labs
 

Offline ledtester

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Re: Looking for programmable clock generator IC, 1 Hz - 20 MHz
« Reply #2 on: August 28, 2020, 12:03:29 am »
The Si5351a is also widely available as a module, eg:

- https://www.adafruit.com/product/2045
- https://www.aliexpress.com/item/4000329085074.html
- https://www.ebay.com/itm/Si5351A-I2C-25MHZ-Clock-Generator-Breakout-Board-8KHz-to-160MHz-for-ArduinoRPA/313163663132

Quote
There is room for variation in the minimum frequency, but I need to get reasonably close to DC, and all of the affordable clock generator chips that I could find so far start at >1 kHz.

You could route the signal through a divider for lower frequencies.
« Last Edit: August 28, 2020, 12:08:03 am by ledtester »
 

Offline Renate

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Re: Looking for programmable clock generator IC, 1 Hz - 20 MHz
« Reply #3 on: August 28, 2020, 12:13:42 am »
Quote from: Si5351 datasheet
Generates up to 8 non-integer-related frequencies from 2.5 kHz to 200 MHz

For the low frequencies you might need a phase accumulator DDS.
I like the AD9850, but that's a bit pricier.
 

Offline ledtester

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Re: Looking for programmable clock generator IC, 1 Hz - 20 MHz
« Reply #4 on: August 28, 2020, 01:39:19 am »
For low frequency clocks you could just program a microcontroller to be a phase accumulator DDS - so the hardware cost might be zero if you have a spare uC board lying around.

For some pointers about this approach google "AVR DDS". The code and circuitry becomes a lot simpler if you just want to output a clock signal.
« Last Edit: August 28, 2020, 01:46:19 am by ledtester »
 

Offline andybrandiTopic starter

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Re: Looking for programmable clock generator IC, 1 Hz - 20 MHz
« Reply #5 on: September 01, 2020, 02:26:12 pm »
Thanks for the suggestions everyone. The Si5351 seems to be a good choice for the higher frequencies, and I should be able to hack the Atmega timer to act as a variable frequency divider.

Phase accumulator DDS is an interesting concept, thanks for bringing that up. It would certainly work well for the lower frequencies, but seems a bit overkill for such a simple clock signal. Still it's a good fallback option since I will have to use a dual approach to accommodate the lower frequencies anyway.
 

Offline HB9EVI

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Re: Looking for programmable clock generator IC, 1 Hz - 20 MHz
« Reply #6 on: September 01, 2020, 02:38:31 pm »
+1 for the SI5351

it's a good choice for many purposes; the C variant allows other reference clocks than 25/27MHz, so it can be fed with a 10MHz OCXO (e.g. GPS disciplined).
my almost finished GPSDO uses 2 SI5351C for altogether 4 independent variable clock outputs (I'm using only 2 output, since there are only 2 independent PLLs to not use the fractional part of the multisynth dividers)
 


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