HFA3783IN96 INTERSIL [Intersil Corporation], HFA3783IN96 Datasheet - Page 17

• Manufacturer Part Number: HFA3783IN96
• Description: I/Q Modulator/Demodulator and Synthesizer
• Manufacturer: INTERSIL [Intersil Corporation]

PLL
The HFA3783 includes a classical architecture Phase Lock
Loop circuit with a three wire serial control interface to be
used with an external VCO. Figure 4 depicts a simplified
block diagram of the PLL. It consists of a programmable “R”
counter used to divide down the frequency of a very stable
reference signal up to 50MHz to a phase comparator. A
couple of counters (“A” and “B”) with a front end prescaler
(“P or P+1”), with dual modulus control, divides down the
frequency of an external VCO signal to the same phase
comparator. The comparator controls a charge pump circuit
and an external loop filter closes the loop for VCO control.
The VCO frequency dividing chain works with a dual
modulus control as follows: At the beginning of a count
cycle, and if the A counter is programmed with a value
greater than zero, the prescaler is set to a division ratio of
(P+1) where P can take programmable values of 16 or 32.
[P*B+A]
1/2V
VCO
REF
R
CC
FIGURE 5. CHARGE PUMP OUTPUT FOR TWO SLIGHTLY DIFFERENT FREQUENCY SIGNALS
REF_IN
PIN 14
17
R COUNTER
TO
DC OFFSET
CAL
R
FIGURE 4. PLL SIMPLIFIED BLOCK DIAGRAM
ISOURCE
V
CP_D0
PIN 22
HFA3783
ISINK
RESET
Notice that the prescaler output signal is always fed
simultaneously to both A and B counters. Upon filling
counter A, the prescaler division ratio becomes P and the B
counter continues on its own with A in standby. This process
is known as “pulse swallowing”. The expression B-A (counts)
is the remainder of counts carried out by the B counter after
A is full. Both A and B counters are reset at the end of the
counting cycle when B fills up. As a result, the total count or
division ratio used for the VCO signal is A*(P+1) + (B-A)*P
which simplifies to [P*B+A]. (A and B counters are referred
as the “N” counter).
The Charge Pump (current source/sink) has 4
programmable current settings. This variation allows the
user to change the reference frequency for different
objectives without changing the loop filter components. The
user can program the charge pump sign based on the
direction of increase or decrease of the VCO frequency. The
N COUNTER
RESET
A
B
DUAL MODULUS
VCONTROL
PRESCALER
CONTROL
P/P+1
VCO
LO_IN+
PIN 27
OR 26