xr215a Exar Corporation, xr215a Datasheet - Page 6

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

SYSTEM DESCRIPTION
The XR-215A monolithic PLL system consists of a
balanced phase comparator, a highly stable voltage-
controlled oscillator (VCO) and a high speed operational
amplifier. The phase comparator outputs are internally
connected to the VCO inputs and to the noninverting input
of the operational amplifier. A self-contained PLL System
is formed by simply AC coupling the VCO output to either
of the phase comparator inputs and adding a low-pass
filter to the phase comparator output terminals.
The VCO section has frequency sweep, on-off keying,
sync, and digital programming capabilities. Its frequency
is highly stable and is determined by a single external
capacitor. The operational amplifier can be used for audio
preamplification in FM detector applications or as a high
speed sense amplifier (or comparator) in FSK
demodulation.
DESCRIPTION OF CIRCUIT CONTROLS
Phase Comparator Inputs (Pins 4 and 6)
One input to the phase comparator is used as the signal
input. The remaining input should be AC coupled to the
6
XR-215A
Rev. 1.01
5
3
4
Figure 2. Equivalent Schematic Diagram
2
11
6
VCO output (pin 15) to complete the PLL (see Figure 3 ).
For split supply operation, these inputs are biased from
ground as shown in Figure 4. For single supply operation,
a resistive bias string similar to that shown in Figure 3
should be used to set the bias level at approximately
V
nominally 8 A.
Phase Comparator Bias (Pin 5)
This terminal should be DC biased as shown in Figure 3
and Figure 4 , and AC grounded with a bypass capacitor.
Phase Comparator Outputs (Pins 2 and 3)
The low frequency (or DC) voltage across these pins
corresponds to the phase difference between the two
signals at the phase comparator inputs (pins 4 and 6). The
phase comparator outputs are internally connected to the
VCO control terminals (see Figure 2. ) One of the outputs
(pin 3) is internally connected to the noninverting input of
the operational amplifier. The low-pass filter is achieved
by connecting an RC network to the phase comparator
outputs as shown in Figure 15.
CC
14 13
/2. The DC bias current at these terminals is
10
12
15
1
7
16
9
8