Circuit Description - Sony CCU-590 Maintenance Manual

3-2. Circuit Description

DM-140 Board
The DM-140 board demodulates Y, R-Y, B-Y, CAM SYNC, and SKIN GATE signals.
The multiplexed signal is separated into power voltage and the RF signal on the IO-214 board. The RF
signal is transferred to the MPX filter on the DM-140 board where the Y RF signal and the CHROMA RF
signal are extracted. These signals are then demodulated to be used as each signal.
This board consists of cable length detector circuit, cable compensation circuit, and their demodulator
circuit.
The cable length is detected from the amplitude of Y modulation wave. Then compensation of amplitude
and phase in accordance with respective Y and color difference modulation waves is carried out in the
cable compensation circuit. These signals are then demodulated in the demodulator circuit.
Cable Compensation Circuit
This circuit comprises 4-stage phase equalizers and amplifiers for compensation of Y, R-Y, and B-Y
modulation waves respectively to compensate attenuation or phase delay of modulation waves due to
cables. When the comparator circuit judges Y compensation circuit output level as insufficient compensa-
tion, the compensation amplifier is activated to amplify the output level. As long as insufficient compen-
sation continues, further compensation is added until signals become adequate.
The R-Y or B-Y compensation circuit, with the same structure as the Y compensation circuit, compen-
sates each signal by interlocking with the Y compensation circuit.
Cable Length Detector Circuit
This circuit determines whether the amplitude of Y compensation circuit output is adequate for demodu-
lation or not. If inadequate, this circuit controls the Y, R-Y, and B-Y compensation circuits to add further
compensation. In order to determine whether compensation is adequate or not, this circuit amplifies the Y
compensation circuit output, peak-holds the output amplitude, and then compares the DC value with the
reference voltage. If the amplitude is inadequate level, this circuit adds further compensation to the signal
by controlling applicable compensation circuit.
Y Demodulator Circuit
The Y signal is demodulated by the demodulator using a carrier whose phase is the same as the Y modu-
lation wave. The demodulated Y signal passes through the amplifier and the buffer, and is then trans-
ferred to the low pass filter (LPF) where the signal is clamped and output after its unnecessary 22.5 MHz
carrier component is eliminated. The CAM SYNC and SKIN GATE signals are also demodulated in the
same way by a carrier whose phase is different (by 90 degrees) from the Y signal.
Color Difference Signal Demodulator Circuit
The B-Y color difference signal is demodulated by the demodulator using a carrier whose phase is the
same as the B-Y modulation wave. The demodulated B-Y signal passes through the amplifier and the
buffer, and is then transferred to the LPF where the signal is clamped and output after its unnecessary 45
MHz carrier component is eliminated. The R-Y signal is also demodulated in the same way by a carrier
whose phase is different (by 90 degrees) from the B-Y signal.
3-2
CCU-590/P/V1(E)