LA7578N 데이터 시트보기 (PDF) - SANYO -> Panasonic
부품명
상세내역
일치하는 목록
LA7578N Datasheet PDF : 18 Pages
| |||
LA7578N
Buzz canceller
The LA7578N’s PIF detector uses the PLL system. The PLL detection system has the following improved characteristics in
comparison with the quasi-synchronous detection system.
(1) Better waveform response characteristics in comparison with the quasi-synchronous detection system.
(2) Harmonic components of the video signal are reduced.
(3) Improved 1/2 IF signal suppression ratio.
(4) Greatly reduced audio buzz.
In general, in the PLL detection system, if the VCO power supply is affected by noise such as flyback pulses (FBP), the VCO
oscillating frequency can be disturbed by the noise component, with a worsening of the buzz characteristics as a result. Therefore,
in order to protect against the effects of VCO power supply fluctuations due to this type of noise in the LA7578N, the VCO
power supply has been regulated to be constant. The explanation below concerns the PLL detector. A typical PLL detection system
consists of the blocks shown in Fig. 1.
Fig. 1 PLL Detector
APC detection by the PLL detector shown in Fig. 1 is accomplished by multiplying the IF signal and the VCO signal by the phase
difference π/2, generating the VCO control voltage. Multiplying by the phase difference π/2 makes it possible to suppress the AM
component; in addition, because VCO is controlled through a low-pass filter (L.P.F), a carrier signal with a good C/N is obtained.
As a result, by using the PLL detection system, the improved characteristics (1) through (4) listed above become possible.
However, because television broadcasts are transmitted using the vestigial sideband system, simply using the PLL detection system
will create the following problems in regard to the audio characteristics. The RF signal that is input from the antenna is converted
to an IF signal by the tuner, and a Nyquist strobe generated by a SAW filter is passed through the corresponding vestigial
sideband . At this point, because the sideband in the region of the picture carrier is eliminated as shown in Fig. 2, the vector
amounts of the upper sideband and the lower sideband differ, generating a phase distortion (θ) in the composite vector amount.
Sound carrier
Fig. 2
No.4037-7/18
Share Link: 