參數(shù)資料
型號: LA7577N
廠商: Sanyo Electric Co.,Ltd.
英文描述: Super-Split,PLL-II VIF and SIF IF Signal Processor for TV/VCRs(用于電視機(jī)/VCR應(yīng)用的IF信號處理(鎖相環(huán)II VIF+SIF)電路)
中文描述: 超斯普利特,鎖相環(huán)-Ⅱ資料表格及SIF中頻信號處理器的電視/錄像機(jī)(用于電視機(jī)/錄像機(jī)應(yīng)用的中頻信號處理(鎖相環(huán)二資料表格強(qiáng)度因子)電路)
文件頁數(shù): 8/16頁
文件大小: 439K
代理商: LA7577N
LA7577N
No. 4037—8/16
This phase distortion is the cause of audio buzz, or
Nyquist buzz, because the VCO synchronizes to the com-
posite vector. A Nyquist buzz cancelation circuit is incor-
porated into the LA7577N to reduce the level of this noise
as shown in Figure 3.
A typical signal with Nyquist buzz is shown in Figure 4
together with the compensating signal generated by the
Nyquist-slope canceler and the resultant signal.
Figure 3. PLL detector with buzz cancelation
Figure 4. Nyquist buzz cancelation waveforms
The circuit shown in Figure 3 is highly effective in sup-
pressing audio buzz caused by the 4.5MHz IF beat signal
in Japanese multiplexed (L
R) audio or American (MTS)
Multichannel TV Sound (L
R) signals.
As buzz cancelation is independent of the PLL loop time
constant, other parameters such as automatic phase control
can be optimized to eliminate interference from flyback
pulses.
Design Notes
FM Detector Output (Pin 1)
The FM detector output is an emitter follower with a
200
series protection resistor as shown in Figure 5.
In multiplex audio applications where pin 1 is connected
to the input of a multiplexed audio decoder, the input
resistance of the decoder can decrease, causing distortion
of the (L
R) signal. In this case, a 5.1k
or larger resis-
tor, R1, should be connected between pin 1 and ground.
Figure 5. FM detector output
In monophonic applications, an RC de-emphasis circuit
should be connected as shown in Figure 6. The time con-
stant is given by R2
×
C.
Figure 6. RC de-emphasis circuit
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