GC3021A Datasheet, PDF (21/38 Pages) Texas Instruments – 3.3V MIXER AND CARRIER REMOVAL CHIP

GC3021A 3.3V MIXER AND CARRIER REMOVAL CHIP
SLWS137A
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
0-15
TYPE
R/W
NAME
FREQ[0:15]
DESCRIPTION
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:
FREQ = _C-^F----^rl-_o-^e---_cq---_ku----^eR---ⁿ--_a-^c--_t-^y-_e- 2³²
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.
Texas Instruments Incorporated
- 19 -
This document contains information which may be changed at any time without notice