Alternative for direct digital synthesizer

Alex:

TI does not have a specific device to handle that requirement.  There are wideband PLL/VCO devices like the LMX2581 that can be programmed down to 50 MHz.  The LMX2571 can be programmed down to 10 MHz.  There may be a clocking generator that can be programmed to lower frequencies, but I was not able to find one on first pass through.

Conceivably you could take an LMX2581 and cascade with a clock buffer/divider device to further divide the output down to support the low specification of 1 MHz.

Another alternative is to re-arrange the transmit architecture for direct sampling.  At 120 MHz, there are high speed DACs that can directly sample to those frequencies.  For example, the DAC3283 samples at 800 MHz and can output signals directly at 120 MHz (and higher) with good spectral performance.

--Russell 

Hello Alex,

The LMK04906 could do the job.  Depending on VCO divider (which can be changed) different high continuous frequencies / lowest possible frequencies can be achieved.  For example:

LMK04906 with VCO divider bypassed can achieve 216.66... MHz to ~2.27 MHz continuous.

With VCO divider = 3; the continuous achievable frequency range is 72.22... MHz to ~0.83 MHz.

The VCO divider may be bypassed or programmed from 2 to 8, all values.

Note, although the LMK04906 is a dual loop capable part, it is possible to run as a single loop.

73,

Timothy