Cypress Semiconductor CY7B991 Scheda tecnica - Pagina 3

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Block Diagram Description

Phase Frequency Detector and Filter
The Phase Frequency Detector and Filter blocks accept inputs
from the reference frequency (REF) input and the feedback (FB)
input and generate correction information to control the
frequency of the Voltage Controlled 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.
It generates a frequency 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 determined by the
FS control pin. The time unit (t
frequency of the device and the level of the FS pin as shown in
Table
1.
Table 1. Frequency Range Select and t
f
(MHz)
NOM
=
t
[2, 3]
U
FS
Min
Max
where N =
LOW
15
30
MID
25
50
HIGH
40
80
Notes
1. For all tri-state inputs, HIGH indicates a connection to VCC, LOW indicates a connection to GND, and MID indicates an open connection. Internal termination circuitry
holds an unconnected input to VCC/2.
2. The level is set on FS is determined by the "normal" operating frequency (fNOM) of the VCO and Time Unit Generator (see
(fNOM) always appears at 1Q0 and the other outputs when they are operated in their undivided modes (see
inputs are fNOM when the output connected to FB is undivided. The frequency of the REF and FB inputs are fNOM/2 or fNOM/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 VCC has reached 4.3V.
Document Number: 38-07138 Rev. *B
) is determined by the operating
U
[1]
Calculation
U
Approximate
1
----------------------- -
×
Frequency (MHz) At
f
N
NOM
Which t
= 1.0 ns
U
44
22.7
26
38.5
16
62.5
Skew Select Matrix
The skew select matrix contains four independent sections. Each
section has two low skew, high fanout drivers (xQ0, xQ1), and
two corresponding three level function select (xF0, xF1) inputs.
Table 2
shows the nine possible output 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
Table 2. Programmable Skew Configurations
Function Selects
1F1, 2F1,
1F0, 2F0,
1Q0, 1Q1,
3F1, 4F1
3F0, 4F0
2Q0, 2Q1
LOW
LOW
–4t
LOW
MID
–3t
LOW
HIGH
–2t
MID
LOW
–1t
MID
MID
0t
MID
HIGH
+1t
HIGH
LOW
+2t
HIGH
MID
+3t
HIGH
HIGH
+4t
Table
2). The frequency appearing at the REF and FB
CY7B991
CY7B992
selected.
U
[1]
Output Functions
3Q0, 3Q1
4Q0, 4Q1
Divide by 2 Divide by 2
U
–6t
–6t
U
U
U
–4t
–4t
U
U
U
–2t
–2t
U
U
U
0t
0t
U
U
U
+2t
+2t
U
U
U
+4t
+4t
U
U
U
+6t
+6t
U
U
U
Divide by 4
Inverted
U
Logic Block
Diagram). Nominal frequency
Page 3 of 19
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