AN178 Philips, AN178 Datasheet - Page 16

• Manufacturer Part Number: AN178
• Description: Modeling the PLL
• Manufacturer: Philips

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DataSheet
Philips Semiconductors
NOISE
The effect of input noise on loop operation is very difficult to predict.
Briefly, the input noise components near the center frequency are
converted to phase noise. When the phase noise becomes so great
that the +905 permissible phse variation is exceeded, the loop drops
out of lock or fails to acquire lock. The best techniques is to actually
apply the anticipated noise amplitude and badwidth to the input and
then perform the capture and lock range measurements as well as
perform operating tests with the anticipated input level and
modulation deviations. By including a small safety factor in the loop
design to compensate for small processing variations, satisfactory
operation can be assured.
1988 Dec
4
U
Modeling the PLL
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Figure 18. Transient Response of PLL Error Voltage to Square Wave Frequency Modulation for Various Damping Conditions
a. Transient Phase Error as an Indication of Damping
a. Underdamped with
c. Overdamped with
Figure 19. Estimating the Damping in a Second-Order PLL
10
0.28
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Damped with
16
b. Ratio of Peak Amplitude to Low Frequency Amplitude of
Error Voltage From Modulating Frequency Response
1.0
d. Highly Overdamped with > 10
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b. Critically
Application note
AN178
SL01029
SL01028