CY7B991
CY7B992
Document #: 38-07138 Rev. ** Page 2 of 15
Block Diagram Description
Phase Frequency Detector and Filter
These two blocks accept inputs from the reference frequency
(REF) input and the feedback (FB) input and generate correc-
tion information to control the frequency of the Voltage-Con-
trolled Oscillator (VCO). These blocks, along with the VCO,
form a Phase-Locked Loop (PLL) that tracks the incoming
REF signal.
VCO and Time Unit Generator
The VCO accepts analog control inputs from the PLL filter
block and generates a frequency that is used by the time unit
generator to create discrete time units that are selected in the
skew select matrix. The operational range of the VCO is de-
termined by the FS control pin. The time unit (t
U
) is determined
by the operating frequency of the device and the level of the
FS pin as shown in Table 1.
Skew Select Matrix
The skew select matrix is comprised of four independent sec-
tions. Each section has two low-skew, high-fanout drivers
(xQ0, xQ1), and two corresponding three-level function select
(xF0, xF1) inputs. Table 2 below shows the nine possible out-
put functions for each section as determined by the function
select inputs. All times are measured with respect to the REF
input assuming that the output connected to the FB input has
0t
U
selected.
Pin Definitions
Signal
Name I/O Description
REF I Reference frequency input. This input supplies the frequency and timing against which all functional
variation is measured.
FB I PLL feedback input (typically connected to one of the eight outputs).
FS I Three-level frequency range select. See Table 1.
1F0, 1F1 I Three-level function select inputs for output pair 1 (1Q0, 1Q1). See Table 2.
2F0, 2F1 I Three-level function select inputs for output pair 2 (2Q0, 2Q1). See Table 2.
3F0, 3F1 I Three-level function select inputs for output pair 3 (3Q0, 3Q1). See Table 2.
4F0, 4F1 I Three-level function select inputs for output pair 4 (4Q0, 4Q1). See Table 2.
TEST I Three-level select. See test mode section under the block diagram descriptions.
1Q0, 1Q1 O Output pair 1. See Table 2.
2Q0, 2Q1 O Output pair 2. See Table 2.
3Q0, 3Q1 O Output pair 3. See Table 2.
4Q0, 4Q1 O Output pair 4. See Table 2.
V
CCN
PWR Power supply for output drivers.
V
CCQ
PWR Power supply for internal circuitry.
GND PWR Ground.
Table 1. Frequency Range Select and t
U
Calculation
[1]
FS
[2, 3]
f
NOM
(MHz)
where N =
Approximate
Frequency (MHz) At
Which t
U
= 1.0 nsMin. Max.
LOW 15 30 44 22.7
MID 25 50 26 38.5
HIGH 40 80 16 62.5
t
U
1
f
NOM
N×
------------------------=
Table 2. Programmable Skew Configurations
[1]
Function Selects Output Functions
1F1, 2F1,
3F1, 4F1
1F0, 2F0,
3F0, 4F0
1Q0, 1Q1,
2Q0, 2Q1 3Q0, 3Q1 4Q0, 4Q1
LOW LOW –4t
U
Divide by 2 Divide by 2
LOW MID –3t
U
–6t
U
–6t
U
LOW HIGH –2t
U
–4t
U
–4t
U
MID LOW –1t
U
–2t
U
–2t
U
MID MID 0t
U
0t
U
0t
U
MID HIGH +1t
U
+2t
U
+2t
U
HIGH LOW +2t
U
+4t
U
+4t
U
HIGH MID +3t
U
+6t
U
+6t
U
HIGH HIGH +4t
U
Divide by 4 Inverted
Notes:
1. For all three-state inputs, HIGH indicates a connection to V
CC
, LOW
indicates a connection to GND, and MID indicates an open connection.
Internal termination circuitry holds an unconnected input to V
CC
/2.
2. The level to be set on FS is determined by the “normal” operating fre-
quency (f
NOM
) of the V
CO
and Time Unit Generator (see Logic Block
Diagram). Nominal frequency (f
NOM
) always appears at 1Q0 and the
other outputs when they are operated in their undivided modes (see
Table 2). The frequency appearing at the REF and FB inputs will be f
NOM
when the output connected to FB is undivided. The frequency of the REF
and FB inputs will be f
NOM
/2 or f
NOM
/4 when the part is configured for a
frequency multiplication by using a divided output as the FB input.
3. When the FS pin is selected HIGH, the REF input must not transition
upon power-up until V
CC
has reached 4.3V.
