XR215A Datasheet, PDF (19/32 Pages) Exar Corporation – Monolithic Phase-Locked Loop

XR-215A
FM
Input
Cc
R₀
R_x
5K
0.1mF
+12V
5K
0.1mF
2K
2K
U1
5
6 Phase
Comp.
16 V_CC
4
11
XR-215A
Cc
12
15
2K
10
V_EE
9 13
C₀
Op
8
Amp
14 2 3 1 7
300pF
8K
7.5K
C₁ C₁
Volume
R_F ^Control
R_P 10K
Cc Coupling Capacitor
Demodulated
Output
10nF (De-Emphasis)
50 50
Figure 16. Circuit Connection for FM Demodulation
APPLICATIONS INFORMATION
FM Demodulation
Figure 16 shows the external circuit connections to the XR-215A for frequency-selective FM demodulation. The choice
of C₀ is determined by the FM carrier frequency (see Figure 8.) The low-pass filter capacitor C₁ is determined by the
selectivity requirements. For carrier frequencies of 1 to 10MHz, C₁ is in the range of 10⋅C₀ to 30⋅C₀. The feedback
resistor R_F can be used as a “volume-control” adjustment to set the amplitude of the demodulated output. The
demodulated output amplitude is proportional to the FM deviation and to resistors R₀ and R_F for +1% FM deviation it can
be approximated as:
ǒ Ǔ V_OUT [ R₀R_F
1
)
0.6
R_X
mV, rms
where all resistors are in kW and R_X is the range extension resistor connected across pins 9 and 10. For circuit operation
below 5MHz, R_X can be omitted. For operation above 5MHz, R_X  750W is recommended.
Typical output signal/noise ratio and harmonic distortion are shown in Figure 17 and Figure 18 as a function of FM
deviation, for the component values shown in Figure 5.
Rev. 1.01
19