LMX2595: Reference clock for LMX2595

Teach Me

Expert 1940 points

Part Number: LMX2595
Other Parts Discussed in Thread: LMX2571, LMX2572

Hi TI Experts,

My customer need an adjustable reference generator with good phase noise to remove the integer boundary spurs.

They need 200 MHz spur free bandwidth from the LMX2595. They are looking for a clean configurable clock so they can avoid crosstalk spur and IBS to get spur free performance across 200 MHz.

Detail requirements as below:

- Is this signal source for a mixer?

It will either be LO for mixer for modulated signal or direct to output stages as CW signal source.

- What frequency range?
10 MHz - 19 GHz

- What phase noise spec?
Phase noise is not the issue. We want to remove IBS, x-talk and other spurs. We found that we cannot do it with a fixed frequency clock. We're targetting 90 dBc SFDR across at least 200 MHz of usable bandwidth centered on the LO frequency. That being said, system phase noise should be ~ -90 dBc @10kHz.

- What reference will be used?

A 10 MHz external OXCO will be used as system clock.

Can TI please advice the suitable part in this case.

Thanks,

Br,

Teach Me

over 7 years ago

0 Dean Banerjee over 7 years ago

TI__Mastermind 28011 points

Teach Me,

If noise is not too critical, try the LMX2571, or if it is, maybe the LMX2572 is better because it has a low noise input doubler.

Regards,
Dean

0 Teach Me over 7 years ago in reply to Dean Banerjee

Expert 1940 points

Hi Dean,

We already fixed the pcba for LMX2595 which is not able to change at the moment.
Thus, we need a clock reference generator to feedback into the LMX2595.
It also must be able to reduce the sporadic frequency spur before entering LMX2595.

The overall configuration as below:

Main board (frequency generator) --> Clock reference generator --> LMX2595

The clock reference generator must able to generate 200Mhz [minimum] spur free bandwidth with a step of 1Mhz.
Detail specification please refer above post.

Please do advice.

Thanks,
Br,
Teach Me

0 Dean Banerjee over 7 years ago in reply to Teach Me

TI__Mastermind 28011 points

Teach Me,

What I was proposing was this:

10 MHz Reference -> LMX2571/72 -> LMX2595

If you use a PLL based approach, this seems simplest to me; I have seen this done before.

Some other approaches could be:

1. Have a bank of XOs and a MUX

2. Take a device like the LMK048xx (assuming you are clocking other things with it) and then change the frequency from there.

3. Realize that the LMX2595 has a programmable input multiplier that can multiply up to 7 that is intended for the same spur avoidance you talk about. Now I agree that doing the multiplication off-chip might be more effective, but his multiplier might be worth a look.

Regards,
Dean

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LMX2595: Reference clock for LMX2595