ADF4116 datasheet(9/20 Pages) AD

9 / 20 page

ADF4116/ADF4117/ADF4118

–9–

REV. 0

–60

–80

–90

–70

TEMPERATURE – C

20406080

100

VDD = 3V

VP = 5V

–100

Figure 19. ADF4118 Reference Spurs vs. Temperature

(836 MHz, 30 kHz, 3 kHz)

CIRCUIT DESCRIPTION

REFERENCE INPUT SECTION

The reference input stage is shown below in Figure 21. SW1

and SW2 are normally-closed switches. SW3 is normally-open.

When power-down is initiated, SW3 is closed and SW1 and SW2

are opened. This ensures that there is no loading of the REFIN

pin on power-down.

BUFFER

TO R COUNTER

REFIN

100k

SW2

SW3

SW1

POWER-DOWN

CONTROL

Figure 21. Reference Input Stage

RF INPUT STAGE

The RF input stage is shown in Figure 22. It is followed by a 2-

stage limiting ampliﬁer to generate the CML clock levels needed

for the prescaler.

AVDD

AGND

500

1.6V

BIAS

GENERATOR

RFINA

RFINB

Figure 22. RF Input Stage

PRESCALER (P/P + 1)

The dual modulus prescale (P/P + 1), along with the A and B

counters, enables the large division ratio, N, to be realized, (N =

PB + A). The dual-modulus prescaler takes the CML clock

from the RF input stage and divides it down to a manageable

frequency for the CMOS A and B counters. The prescaler is

programmable. It can be set in software to 8/9 for the

ADF4116, and set to 32/33 for the ADF4117 and ADF4118.

It is based on a synchronous 4/5 core.

A AND B COUNTERS

The A and B CMOS counters combine with the dual modulus

prescaler to allow a wide ranging division ratio in the PLL

feedback counter. The counters are speciﬁed to work when the

prescaler output is 200 MHz or less.

Pulse Swallow Function

The A and B counters, in conjunction with the dual modulus

prescaler make it possible to generate output frequencies which

are spaced only by the Reference Frequency divided by R. The

equation for the VCO frequency is as follows:

fVCO = [(P

× B) + A] × f

REFIN/R

fVCO

Output Frequency of external voltage controlled oscilla-

tor (VCO).

Preset modulus of dual modulus prescaler.

Preset Divide Ratio of binary 13-bit counter (3 to 8191).

Preset Divide Ratio of binary 5-bit swallow counter

(0 to 31).

fREFIN Output frequency of the external reference frequency

oscillator.

Preset divide ratio of binary 14-bit programmable refer-

ence counter (1 to 16383).

R COUNTER

The 14-bit R counter allows the input reference frequency to be

divided down to produce the input clock to the phase frequency

detector (PFD). Division ratios from 1 to 16,383 are allowed.

13-BIT B

COUNTER

5-BIT A

COUNTER

PRESCALER

P/P + 1

FROM RF

INPUT STAGE

MODULUS

CONTROL

N = BP + A

LOAD

TO PFD

Figure 23. A and B Counters

0.0

PRESCALER OUTPUT FREQUENCY – MHz

100

150

200

0.5

1.0

1.5

2.0

2.5

3.0

Figure 20. DIDD vs. Prescaler Output Frequency

(ADF4116, ADF4117, ADF4118)

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