
IDT / ICS 700MHZ, 3.3V LVPECL FREQUENCY SYNTHESIZER
2
ICS8430B-71 REV A NOVEMBER 20, 2006
ICS8430B-71
700MHZ, CRYSTAL INTERFACE/LVCMOS-TO-3.3V LVPECL FREQUENCY SYNTHESIZER
default state that will automatically occur during power-up. The
TEST output is LOW when operating in the parallel input mode.
The relationship between the VCO frequency, the crystal fre-
quency and the M divider is defined as follows:
The M value and the required values of M0 through M8 are
shown in Table 3B, Programmable VCO Frequency Function
Table. Valid M values for which the PLL will achieve lock for a
16MHz reference are defined as 125
≤ M ≤ 350. The frequency
out is defined as follows:
Ser ial oper ation occurs when nP_LOAD is HIGH and
S_LOAD is LOW. The shift register is loaded by sampling
the S_DATA bits with the rising edge of S_CLOCK. The con-
tents of the shift register are loaded into the M divider and
N output divider when S_LOAD transitions from LOW-to-
HIGH. The M divide and N output divide values are latched
on the HIGH-to-LOW transition of S_LOAD. If S_LOAD is
held HIGH, data at the S_DATA input is passed directly to
the M divider and N output divider on each rising edge of
S_CLOCK. The serial mode can be used to program the M
and N bits and test bits T1 and T0. The inter nal registers T0
and T1 determine the state of the TEST output as follows:
NOTE: The functional description that follows describes opera-
tion using a 16MHz crystal. Valid PLL loop divider values for
different crystal or input frequencies are defined in the Input
Frequency Characteristics, Table 5, NOTE 1.
The ICS8430B-71 features a fully integrated PLL and therefore
requires no external components for setting the loop bandwidth.
A parallel-resonant, fundamental crystal is used as the input to
the on-chip oscillator. The output of the oscillator is divided by
16 prior to the phase detector. With a 16MHz crystal, this pro-
vides a 1MHz reference frequency. The VCO of the PLL oper-
ates over a range of 250MHz to 700MHz. The output of the M
divider is also applied to the phase detector.
The phase detector and the M divider force the VCO output
frequency to be 2M times the reference frequency by adjusting
the VCO control voltage. Note that for some values of M (either
too high or too low), the PLL will not achieve lock. The output
of the VCO is scaled by a divider prior to being sent to each of
the LVPECL output buffers. The divider provides a 50% output
duty cycle.
The programmable features of the ICS8430B-71 support two
input modes to program the M divider and N output divider.
The two input operational modes are parallel and serial.
Figure
1 shows the timing diagram for each mode. In parallel mode,
the nP_LOAD input is initially LOW. The data on inputs M0
through M8 and N0 through N2 is passed directly to the M
divider and N output divider. On the LOW-to-HIGH transition of
the nP_LOAD input, the data is latched and the M divider re-
mains loaded until the next LOW transition on nP_LOAD or
until a serial event occurs. As a result, the M and N bits can be
hardwired to set the M divider and N output divider to a specific
FUNCTIONAL DESCRIPTION
N
fout = fVCO =
16
2M
fxtal x
N
16
fVCO =
fxtal x 2M
T1
T0
TEST Output
00
LOW
0
1
S_Data clocked into register
1
0
Output of M divider
1
CMOS Fout
FIGURE 1. PARALLEL & SERIAL LOAD OPERATIONS
Time
SERIAL LOADING
PARALLEL LOADING
t
S
t
H
t
S
t
H
t
S
M, N
T1
T0
N2
N1
N0
M8
M7
M6
M5
M4
M3
M2
M1
M0
S_CLOCK
S_DATA
S_LOAD
nP_LOAD
M0:M8, N0:N2
nP_LOAD
S_LOAD