LMX2355TM datasheet(19/23 Pages) NSC

19 / 23 page

Programming Description (Continued)

5.3 QUADRATURE MODULUS PRESCALER

The LMX2354 contains a quadrature modulus prescaler, consisting of a prescaler, A counter, B counter and C counter. Once the

N value is known, the A, B, and C values can be calculated by:

C = N div P

B=(N–C

•P) div 4

A = N mod 4

For the divide ratio to be legal, it is also required:

C> =max {A, B} + 2

fvco = [N + F] x [fosc/R]

N=P

• C+4•B+ A

Fractional ratio (contents of FRAC_CNTR divided by the fractional modulus)

vco: Output frequency of external voltage controlled oscillator (VCO)

Preset value of the C counter

Preset value of the B counter

Preset value of the A counter

osc: Output frequency of the external reference frequency oscillator

Preset divide ratio of binary 15-bit programmable reference counter (3 to 32,767)

Preset modulus of quadrature modulus prescaler

8/9/12/13

550 MHz–1.2 GHz

16/17/20/21

1.2 GHz–2.5 GHz

5.4 SERIAL DATA INPUT TIMING

20004803

Note: Data shifted into register on clock rising edge. Data is shifted in MSB first.

TEST CONDITIONS: The Serial Data Input Timing is tested using a symmetrical waveform around VCC/2. The test waveform has an edge rate of 0.6 V/ns

with amplitudes of 2.2V @ VCC=2.7V and 2.6V @ VCC = 5.5V.

LMX2355TM Datasheet(PDF) 19 Page - National Semiconductor (TI)