µPC1876

14

Data Sheet S11666EJ4V0DS00

2.1

Stereo Demodulation Block

(1) Stereo LPF

Filter eliminates the Sub Audio Program (SAP) signal (5 fH) and telemetry signal (6.5 fH) residing anywhere around

5 to 6 fH.

The internal L–R demodulator, which uses the double-balanced circuit, demodulates L–R signal by multiplication

of L–R signal with the signal at L–R carrier frequency (2 fH). The L–R signal tends to be interfered by the 6 fH

signal because a square waveform is used as the switching carrier in this method. To eliminate the interference,

the

µPC1876 incorporates 5 fH and 6 fH traps.

Adjust the current value output from the FLTA pin for the filter response.

(2) Stereo phase comparator

The 8 fH signal generated at the stereo VCO is divided by 8 (4

× 2) and then multiplies it with the pilot signal passed

through the stereo LPF. The two signals differ from each other by 90 degrees in terms of phase.

The resistor and capacitor connected to the

φD1 and φD2 pins form a filter which smoothes the phase error signal

output from the phase comparator, converting the error signal to the DC voltage. When the voltage difference

between the

φ D1 and φD2 pins becomes 0 V (strictly speaking, not 0 V by the internal offset voltage), the stereo

VCO runs at 8 fH.

The lag/lead filter externally connected to the

φD1, φD2 pins determines the capture range.

(3) Stereo VCO

Runs at 8 fH with the internal capacitor. Adjust the current value output from the STVA pin for the frequency.

(4) Divider (Flip-flop)

Produces the inphase fH signal and the fH signal which is different 90 degrees from the input pilot signal by dividing

the 8 fH frequency by 4

× 2 from the stereo VCO.

(5) Pilot discrimination phase comparator (Level detector)

Multiplies the pilot signal from the COM pin with the inphase fH signal from the divider. The produced signal is

applied to the external filter connected to the PD1, PD2 pins. The signal is smoothed out to make DC voltage

for judging whether to turn on or off the stereo LED.

(6) Pilot canceller

The fH signal from the divider is added in the stereo signal at the resistor matrix depending on the level of the

input pilot signal to cancel the pilot signal.

(7) L+R LPF

This LPF, having traps at fH and 24 kHz each, allows only the monaural signal to pass through. The filter response

is adjusted by the current value output from the FLTA pin.

(8) De-emphasis

75

µs de-emphasis filter for the monaural signal. The filter response is adjusted by the current value output from

the FLTA pin.

(9) L–R AM demodulator

Demodulates the L–R AM-DSB modulated signal by multiplying with the 2fH signal which is synchronized to the

pilot signal. The 2 fH square wave is used as the switching carrier.