XR2212 Exar Corporation, XR2212 Datasheet - Page 10

• Manufacturer Part Number: XR2212
• Description: Precision Phase-Locked Loop
• Manufacturer: Exar Corporation

Design Equations
(See Figure 3 and Figure 10 for definition of
components.)
1. VCO Center Frequency, f
2. Internal Reference Voltage, V
3. Loop Low-Pass Filter Time Constant, : = R
4. Loop Damping, :
5. Loop Tracking Bandwidth,
6. Phase Detector Conversion Gain, K : (K
7. VCO Conversion Gain, K
XR-2212
Pin 11)
V
where N is the external frequency divider modular
(See 2). If no divider is used, N = 1.
differential DC voltage across Pins 10 and 11, per unit
of phase error at phase-detector input)
K = -2V
change in VCO frequency, per unit of DC voltage
change at Pin 10. It is the reciprocal of the slope of
conversion characteristics shown in Figure 10 ).
K
Rev. 2.01
REF
0
= -1/V
= V
REF
CC
REF
/2 - 650mV
/ volts/radian
C
0.25
0
R
1
Hz/V
NC
C
1
0
0
: f
0
: (K
0
REF
= 1/R
f/f
0
0
: f/f
(measured at
is the amount of
0
C
0
0
= R
Hz
0
/R
1
is the
C
1
1
10
8. Total Loop Gain, K
9. Peak Phase-Detector Current, I
APPLICATION INFORMATION
FM Demodulation
XR-2212 can be used as a linear FM demodulator for both
narrow-band and wide-band FM signals. The generalized
circuit connection for this application is shown in
Figure 11 , where the VCO output (Pin 5) is directly
connected to the phase detector input (Pin 16). The
demodulated signal is obtained at phase detector output
(Pin 10). In the circuit connection of Figure 10, the op amp
section of XR-2212 is used as a buffer amplifier to provide
both additional voltage amplification as well as current
drive capability. Thus, the demodulated output signal
available at the op amp output (Pin 8) is fully buffered from
the rest of the circuit.
In the circuit of Figure 11 , R
frequency, R
low-pass filter time constant. Op amp feedback resistors
R
F
and R
K
I
A
T
= V
= 2 K K
C
REF
set the voltage gain of the amplifier section.
1
(volts)/25mA
sets the tracking bandwidth, C
0
= 4/C
T
0
R
1
rad/sec/volt
0
C
0
A
set the VCO center
; available at Pin 10.
1
sets the