Andy Peters
Well-known member
I kinda need a simple, high-quality 2-channel ADC with word clock sync that supports the 44.1 kHz and the 48 kHz multiple sampling frequencies. This seems like it's an ideal project for DIY. Except it seems like none of the usual suspects sell a 22.5792 MHz oscillator, at least in non-full-reel quantities.
Silicon Labs has been sending me e-mail updates about their products, including programmable VCXO and XO devices. One product in particular stood out: the Si598 I2C programmable XO (pdf). Using an I2C port, you can set its output to any frequency between 10 MHz and 810 MHz, with what looks to be spectacular jitter specs.
This guy seems to neatly solve a handful of problems. One oscillator covers all of the converter modulator clock frequencies. The same oscillator is used for both master (internal clocking) and slave (external word-clock) modes. You don't need to implement muxes or switches to select the clock source or clock mode.
All you need is a micro with an I2C master and a phase detector (which could be in the micro). Some micro port pins can be used for switch inputs (mode select, sample frequency, whatever). In master mode, the micro just sets the oscillator frequency as desired. In slave mode, the micro handles the phase detector and the loop filter, and sets the oscillator frequency as necessary. (Choose an ADC that has a "master mode" for the I2C, where it takes in the MCLK and generates BCLK and LRCLK, and you don't even have to use an external divider to drive the PLL. Just feed LRCLK into the phase detector.)
I'm trying to get a sample and see what these things cost. Even if they're ten bucks, it might end up being cheaper than two oscillators and two VXCOs or PLLs and whatever else is required to implement the clocking.
-a
Silicon Labs has been sending me e-mail updates about their products, including programmable VCXO and XO devices. One product in particular stood out: the Si598 I2C programmable XO (pdf). Using an I2C port, you can set its output to any frequency between 10 MHz and 810 MHz, with what looks to be spectacular jitter specs.
This guy seems to neatly solve a handful of problems. One oscillator covers all of the converter modulator clock frequencies. The same oscillator is used for both master (internal clocking) and slave (external word-clock) modes. You don't need to implement muxes or switches to select the clock source or clock mode.
All you need is a micro with an I2C master and a phase detector (which could be in the micro). Some micro port pins can be used for switch inputs (mode select, sample frequency, whatever). In master mode, the micro just sets the oscillator frequency as desired. In slave mode, the micro handles the phase detector and the loop filter, and sets the oscillator frequency as necessary. (Choose an ADC that has a "master mode" for the I2C, where it takes in the MCLK and generates BCLK and LRCLK, and you don't even have to use an external divider to drive the PLL. Just feed LRCLK into the phase detector.)
I'm trying to get a sample and see what these things cost. Even if they're ten bucks, it might end up being cheaper than two oscillators and two VXCOs or PLLs and whatever else is required to implement the clocking.
-a