Dear Experts,

My customer is considering to choose ADF4351. Could you please reply to the following question?

**Q1:** We can see "prescaler" (= 4/5 or 8/9) in the ADF4351 datasheet but cannot see any equation with “prescaler” in the ADF4351 datasheet.

What frequency does the "prescaler" in ADF4351 impact on?

I suppose that the prescaler (P) value will impact on PFD frequency (f_PFD) as shown in the following equation. Is it correct?

Note: "P" in the above equation means "prescaler" (= 4/5 or 8/9) in ADF4351.

The following is just a reference for the RFout frequency calculation:

Could you please advise my customer about your reply to the above question?

Thanks and regards.

The prescaler is part of the N counter.

The N counter comprises the Prescaler and some integer values, which are modulated by the sigma delta modulator to implement fractional N.

The prescler is essentially transparent, except in some cases, outlined below:

The dual-modulus prescaler (P/P + 1), along with the INT, FRAC, and MOD values, determines the overall division ratio from the VCO output to the PFD input. The PR1 bit (DB27) in Register 1 sets the prescaler value. Operating at CML levels, the prescaler takes the clock from the VCO output and divides it down for the counters. The prescaler is based on a synchronous 4/5 core. When the prescaler is set to 4/5, the maximum RF frequency allowed is 3.6 GHz. Therefore, when operating the ADF4351 above 3.6 GHz, the prescaler must be set to 8/9. The prescaler limits the INT value as follows: • Prescaler = 4/5: NMIN = 23 • Prescaler = 8/9: NMIN = 75.