xr215a Exar Corporation, xr215a Datasheet - Page 17

• Manufacturer Part Number: xr215a
• Description: Monolithic Phase-locked Loop
• Manufacturer: Exar Corporation

Phase Comparator Gain K
The output voltage from the phase comparator per radian
of phase difference at the phase comparator inputs (pins
4 and 6). The units are volts/radians. (See Figure 9. )
VCO Conversion Gain Ko
The VCO voltage-to-frequency conversion gain is
determined by the choice of timing capacitor C
control resistor, R
and 12. It can be expressed as:
where C
recommended values for R
Rev. 1.01
Figure 14. Linearized Model of a PLL as a
0
s
is in F and R
-
Negative Feedback System
0
K
0
0
connected externally across pins 11
C
700
0
0
K
R
is in k . For most applications,
d
0
0
d
(radians/sec/volt)
range from 1k
Ko
s
F(s)
to 10k .
0
and gain
17
Lock Range ( wL)
The range of frequencies in the vicinity of f
the PLL can maintain lock with an input signal. It is also
known as the “tracking” or “holding” range. If saturation or
limiting does not occur, the lock range is equal to the loop
gain, i.e.
Capture Range ( wC)
The band of frequencies in the vicinity of f
can establish or acquire lock with an input signal. It is also
known as the “acquisition” range. It is always smaller than
the lock range and is related to the low-pass filter
bandwidth. It can be approximated by a parametric
equation of the form:
where |F(j
at
where T
Amplifier Gain AV
The voltage gain of the amplifier section is determined by
feedback resistors R
(2,1) respectively. (See Figure 3 and Figure 4. ) It is given
by:
where R
=
1
1
C
is the filter time constant.
is the (6k ) internal impedance at pin 2.
. For a simple lag filter, it can be expressed as:
L
C
= K
| is the low-pass filter magnitude response
T
A
= K
V
C
C
F
d
and Rp between pins (8,1) and
K
R
o
.
1
–R
L
T
1
|F(j
F
L
R
XR-215A
P
C
)|
o
where the PLL
o
, over which