ACD2203 Datasheet, PDF (15/24 Pages) ANADIGICS, Inc – CATV/TV/Video Downconverter with Dual Synthesizer

ACD2203
Synthesizer Programming Example
The following example for programming the two synthesizers in the dual PLL details the calculations used
to determine the required value of each bit in all four registers:
Requirements
Desired CATV input channel: “HHH” - 499.25 MHz picture carrier (501 MHz digital channel center frequency)
(Second) IF picture carrier output frequency: 45.75 MHz (44 MHz digital channel center frequency)
First IF frequency: 1087.75 MHz (recommended)
Phase detector comparison frequency for down converter (also tuning increment): 62.5 KHz
Phase detector comparison frequency for up converter: 250 KHz
Crystal reference oscillator frequency: 4 MHz
Calculation of Reference Divider Values
The value for each reference divider is calculated by dividing the reference oscillator frequency by the desired
phase detector comparison frequency:
R = fOSC / fPD
For the down converter, the 4 MHz crystal oscillator frequency and the 62.5 KHz phase detector comparison
frequency are used to yield RPLL2 = 4 MHz / 62.5 KHz = 64, and so the bit values for the down converter
R counter are RPLL2 = 000000001000000.
For the up converter, the 4 MHz crystal oscillator frequency and the 250 KHz phase detector comparison
frequency are used to yield RPLL1 = 4 MHz / 250 KHz = 16, and so the bit values for the up converter R counter
are RPLL1 = 000000000010000.
Calculation of Main Divider Values
The values for the A and B counters are determined by the desired VCO output frequency for the local
oscillator and the phase detector comparison frequency:
N = f_VCO / f _PD
B = trunc(N / P)
A = N - (B x P)
The down converter local oscillator frequency will be 1087.75 MHz - 45.75 MHz = 1042 MHz in this example.
The main divider ratio for the down converter, then, is NPLL2 = 1042 MHz / 62.5 KHz = 16672. Since P = 64 in the
ACD2203, BPLL2 = trunc(16672 / 64) = 260, and APLL2 = 16672 - (260 x 64) = 32. These results give bit values
of BPLL2 = 00100000100 and APLL2 = 0100000 for the B and A counters.
The up converter local oscillator frequency will be 499.25 MHz + 1087.75 MHz = 1587 MHz in this example.
Therefore, NPLL1 = 1587 MHz / 250 KHz = 6348, BPLL1 = trunc(6348 / 64) = 99, and APLL1 = 6348 - (99 x 64) = 12.
These results give bit values of BPLL1 = 00001100011 and APLL1 = 0001100 for the B and A counters.
Phase Detector Polarity
If the VCO for the up converter has a negative slope, the phase detector polarity for PLL1 should be negative,
and D1PLL1 = 1. If the VCO for the down converter has a positive slope, the phase detector polarity for PLL2
should be positive, and D1PLL2 = 0.
In summary, for this example, the four register programming words are shown in Tables 17 and 18 on the
following page.
PRELIMINARY DATA SHEET - Rev 1.3
15
12/2003