Digital Clock Generator IC used as Analog Mixer LO input?

[yakex]

Hi,
I need an analog frequency for mixer LO as 600-1200Mhz. The ultimate frequency of DDS is about 400MHz (AD9910 by ADI), but the CDCE62005 (by TI) ranges from 4.25MHz to 1.175GHz. so I pan to adopt the AD9910 to synthesize a low frequency (about 40Mhz), and applied to the input of CDCE62005, by programming the CDCE62005, the output can achieve the required frequency.
the question is, CDCE62005 is a digital clock IC, does it fit for analog mixer lo sources?
Thanks to anybody.
Yan

 

[jmpac]

Hello,

your mixer is an active or a passive device? Take into account the maximum LO level allowed to the mixer. If the DDS selected has good phase noise (or jitter) for your application, you only have to filter out harmonics with a 5th order low-pass filter till 1.2GHz, however, you'll see with this that the second harmonic of 600MHz is still passing through the filter, thus, due to the high bandwidth of synthesis, I would divide it in two bands (600-900 and 900-1200 MHz, for example) and place two parallel filter switched by an RF switch with good isolation (>20dB)

Regards.

 

[yakex]

Hello,

your mixer is an active or a passive device? Take in account the maximum LO level allowed to the mixer. If the DDS selected has good phase noise (or jitter) for your application, you only have to filter out harmonics with a 5th order low-pass filter till 1.2GHz, however, you'll see with this that the second harmonic of 600MHz is still passing through the filter, thus, due to the high bandwidth of synthesis, I would divide it in two bands (600-900 and 900-1200 MHz, for example) and place two parallel filter switched by an RF switch with good isolation (>20dB)

Regards.

Thank you
my mixer is an passive.
There is no problem about the LO level.
I want to know that is there any additive noise because it is a digital IC usually used as clock source.

 

[RCinFLA]

Most mixers like full switching for LO. Digital is usually lower noise as time spent in linear region is minimized. This assumes the digital power supply isn't common to other noisey digital circuits.

It can get screwed up by poor original oscillator source and how the source oscillator is coupled into digitial logic. You want to get digital going rail to rail in as few stages as possible for ref osc input.

 

[jmpac]

Yakex,
The main noise is due to spurious, phase noise (jitter) and harmonics all generated by a DDS or PLL.
Moreover, for filtering the power supply you can place a typical PI-filter with capacitors and a choke, or even a linear regulator could be placed if your original power supply comes from a buck DC-DC converter (noisy).
Regards.

 

[yakex]

Most mixers like full switching for LO. Digital is usually lower noise as time spent in linear region is minimized. This assumes the digital power supply isn't common to other noisey digital circuits.

It can get screwed up by poor original oscillator source and how the source oscillator is coupled into digitial logic. You want to get digital going rail to rail in as few stages as possible for ref osc input.

"going rail to rail in as few stages as possible for ref osc input. "
What does it mean?
Thank you.
Yakex