XR215A Datasheet, PDF (6/32 Pages) Exar Corporation – Monolithic Phase-Locked Loop

XR-215A
16
3
2
1
8
7
14 13
15
6
4
5
11
12
10
9
Figure 2. Equivalent Schematic Diagram
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
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_CC/2. The DC bias current at these terminals is
nominally 8mA.
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.
Rev. 1.01
6