Texas Instruments Incorporated - 19 -
GC3021A 3.3V MIXER AND CARRIER REMOVAL CHIP SLWS137A
This document contains information which may be changed at any time without notice
4.5 PLL CONTROL REGISTER
The phase lock loop (PLL) phase hold control and filter coefficients are stored in this register. The
suggested default is 028A (HEX) which sets A=10 and B=20 for acquisition, and 038e (HEX) which sets
A=14 and B=28 for tracking.
ADDRESS 5: PLL_REG
BIT
TYPE NAME DESCRIPTION
0-4 R/W A[0:4] The 5 bit “A” coefficient. See Figure 5. The phase error
is multiplied by 2
-A
for A equal to 1 through 31, and is
multiplied by 0 for A equal to 0.
5-9 R/W B[0:4] The 5 bit “B” coefficient. See Figure 5. The phase error
is multiplied by 2
-B
for B equal to 1 through 31, and is
multiplied by 0 for B equal to 0.
10 R/W EXT_ERROR Use the EIN input as the error input to the PLL circuit.
EIN = 0 adds to the phase, EIN = 1 subtracts.
11-14 R/W - unused
15 (MSB) R/W PHASE_HOLD The phase register tracks the value of the phase
increment when this bit is low and holds the last value
when this bit is high.
The A and B coefficients stored in this register are not used until the AB_SYNC is asserted as
described in Section 4.2.
4.6 FREQUENCY WORD REGISTERS
Registers 6 and 7 contain the 32 bit frequency tuning word. The frequency word is added into the
PLL output as shown in Figure 4. Bit 0 is the LSB, bit 31 is the MSB. The suggested default is zero.
ADDRESS 6: FREQ_REG0
BIT
TYPE NAME DESCRIPTION
0-15 R/W FREQ[0:15] 16 LSBs of the frequency word
ADDRESS 7: FREQ_REG1
BIT
TYPE NAME DESCRIPTION
0-15 R/W FREQ[15:31] 16 MSBs of the frequency word
The tuning frequency is specified using the formula:
where “Frequency” is the desired tuning frequency, and “clock rate” is the chip’s clock rate. The FREQ value
stored in these registers are transferred to the PLL circuit when the FREQ_SYNC is asserted as described
in Section 4.2.
FREQ
Frequency
Clock Rate
-----------------------------
2
32
=
