Looking for programmable clock generator IC, 1 Hz - 20 MHz - Page 1
Forum section: electronics / projects

author: andybrandi
author_rank: Contributor
timestamp: August 27, 2020, 10:33:53 pm
content: 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 quantitiesRemarks:- a single output channel is sufficient- no constraints on output or supply voltage levelsAny 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.Thanks!

author: MasterT
author_rank: Frequent Contributor
timestamp: August 27, 2020, 11:42:08 pm
content: In this price range only Si5351 comes to mind,https://www.arrow.com/en/products/si5351a-b06208-gt/silicon-labs

author: ledtester
author_rank: Super Contributor
timestamp: August 28, 2020, 12:03:29 am
content: 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/313163663132QuoteYou could route the signal through a divider for lower frequencies.

author: Renate
author_rank: Super Contributor
timestamp: August 28, 2020, 12:13:42 am
content: Quote from: Si5351 datasheetFor the low frequencies you might need a phase accumulator DDS.I like the AD9850, but that's a bit pricier.

author: ledtester
author_rank: Super Contributor
timestamp: August 28, 2020, 01:39:19 am
content: 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.

author: andybrandi
author_rank: Contributor
timestamp: September 01, 2020, 02:26:12 pm
content: 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.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: September 01, 2020, 02:38:31 pm
content: +1 for the SI5351it'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)