Datasheet
DS_1903_032 73M1903 Data Sheet
Rev. 2.1 13
3 Clock Generation
3.1 Crystal Oscillator and Pre-scaler NCO
The crystal oscillator operates over wide choice of crystals (from 9 MHz to 27 MHz) and it is first input to
an
NCO based pre-scaler (divider) prior to being passed onto an on-chip PLL
Appendix B
. The intent of the pre-
scaler is to convert the crystal oscillator frequency, Fxtal, to a convenient frequency to be used as a
reference frequency, Fref, for the PLL. The NCO pre-scaler requires a set of three numbers to be
entered through the serial port (Pseq[7:0], Prst[2:0] and Pdvsr[2:0]. The PLL also requires 3 numbers as
for programming; Ndvsr[6:0], Nseq[7:0], and Nrst[2:0]. The following is a brief description of the registers
that control the NCOs, PLLs, and sample rates for the 73M1903 IC. The tables show some examples of
the register settings for different clock and sample rates. A more detailed discussion on how these values
are derived can be found in .
3.1.1 Control Register (CTRL 8): Address 08h
Reset State 00h
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Pseq7 Pseq6 Pseq5 Pseq4 Pseq3 Pseq2 Pseq1 Pseq0
This corresponds to the sequence of divisor. If Prst{2:0] =0 this register is ignored.
3.1.2 Control Register (CTRL 9): Address 09h
Reset State 0Ah
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Prst2 Prst1 Prst0 Pdvsr4 Pdvsr3 Pdvsr2 Pdvsr1 Pdvsr0
Prst[2:0] represents the rate at which the sequence register is reset.
Pdvsr[4:0] represents the divisor.
3.1.3 Control Register (CTRL 10): Address 0Ah
Reset State 22h
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Ichp3 Ichp2 Ichp1 Ichp0 FL Kvco2 Kvco1 Kvco0
Kvco2:0 represents the magnitude of Kvco associated with the VCO within PLL. This indicates the center
frequency of the VCO when the control voltage is 1.6 Volts and the slope of the VCO freq versus control
voltage (i.e., Kvco.). FL represents the PLL loop filter settings.
Table 4: Kvco versus Settings at Vc=1.6 V, 25 °C
Kvco2 Kvco1 Kvco0 Fvco Kvco
0 0 0 33 MHz 38 MHz/v
0 0 1 36 MHz 38 MHz/v
0 1 0 44 MHz 40 MHz/v
0 1 1 48 MHz 40 MHz/v
1 0 0 57 MHz 63 MHz/v
1 0 1 61 MHz 63 MHz/v
1 1 0 69 MHz 69 MHz/v
1 1 1 73 MHz 69 MHz/v