lc72134m Sanyo Semiconductor Corporation, lc72134m Datasheet - Page 23

• Manufacturer Part Number: lc72134m
• Description: Dual Pll Frequency Synthesizer For Fm Tuner Systems
• Manufacturer: Sanyo Semiconductor Corporation

Other Items
• Notes on the phase comparator dead zone
When the charge pump is used with one of the ON/ON modes, correction pulses are generated from the charge pump
even if the PLL is locked. As a result, it is easy for the loop to become unstable, and special care is required in
application design. The following problems can occur if an ON/ON mode is used.
— Sidebands may be created by reference frequency leakage.
— Sidebands may be created by low-frequency leakage due to the correction pulse envelope.
Although the loop is more stable when a dead zone is present (i.e. when an OFF/OFF mode is used), a dead band
makes it more difficult to achieve excellent C/N characteristics. On the other hand, while it is easy to achieve good C/N
characteristics when there is no dead zone, achieving good loop stability is difficult. Accordingly, the DZA and DZB
settings, in which there is no dead zone, can be effective in situations where a signal-to-noise ratio of 90 to 100 dB or
higher is required in FM reception, or where it is desirable to increase the pilot margin in AM stereo reception.
However, if such a high signal-to-noise ratio is not required for FM reception, if an adequate pilot margin can be
acquired in AM stereo reception, or if AM stereo is not required, then either DZC or DZD, in which there is a dead
band, should be chosen.
DZ1
0
0
1
1
DZ0
0
1
0
1
Dead band mode
DZC
DZD
DZA
DZB
Charge pump
OFF/OFF
OFF/OFF
ON/ON
ON/ON
LC72134M
≥
Dead band
– –0s
+ +0s
+0s
–0s
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