ADF411X PLL N counter, R counter range

Prescaler choices: 8/9, 16/17, 32/33, 64/65

RF/P <= 200 MHz


The N counter is acutally a dual modulus prescaler that is controlled by the A and B counters. Both A and B counters are toggled each time by the prescaler's output pulses. In operation, the RF signal is divided by P+1 A times and by P (B-A) times. Thus the net division is N=A*(P+1)+(B-A)*P

N= BP + A

A, B Ranges
B = 3 to 8191
A = 0 to 63

R counter range 1 to 16383

ADF411X PLL IC PD polarity

Phase Detector Polarity Bit
0 Negative
1 Positive

For PD=Positive
Ref/R > RF/N, CP sources current, Vt increases
Ref/R < RF/N, CP sinks current, Vt decreases.


For PD=Neg
RF/N > Ref/R, CP sources current, Vt increases
RF/N < Ref/R, CP sinks current, Vt decreases.




**In project, we use a 3200 mhz reference signal into the "RF" input and an IF signal into the "REF" input. The IF is obtained by mixing down or sampling the VCO frequency.** With a passive or non-inverting active loop filter, PD polarity should be Negative.