A multiplexing signal contains the baseband information which as well as or many SCA transmits on the three-dimensional acoustic simulation FM broadcast system (assistance traffic authorization) the channel (Figure 1). This “Design Example” narrated one kind has 19 kHz basic pilot frequency sound low cost method. 19 kHz pilot frequency sound including a baseband signal, but the L R signal and the L-R signal by as central DSBSC (twin sideband quiescent carrier) are composed take 38 kHz. For the receiver correct demodulation signal cabin transmission’s pilot frequency sound and the L-R signal must in an its respective zero crossing synchronization. Moreover, pilot frequency sound’s any distortion can produce the overtone, thus disturbance neighbor signal.
The low distortion’s 19 kHz pilot frequency sound generator and - between the VCC power source’s resistance voltage divider (R1 ~ R11) is composed (Figure by a connection in the VCC power source 2). These resistor’s resistance number must after the weighting in order to provide N=8 the sine wave approximate sampling value. These resistance numbers are quite small, what for is eight channel simulation multiplexer IC1 provides the stable low impedance supply oscillator. Reversible counter IC2 actuates IC1, and enhances 19 kHz pilot frequency sine wave using the sine wave inherent symmetry the precision, reduces its distortion.
In fact, simulation multi-channel multiplexer IC1 serve as a zeroth order maintains the electric circuits, has a frequency is the fSIN N time of Nyquist sampling sine wave as well as take fALIAS as the central several aliasing frequency. fALIAS=m×(2×N×fSINE), in the formula m=1, 2, 3. To the majority application systems, multi-channel multiplexer out-port’s simple passive RC filter sufficiently filters the aliasing frequency code. Binary system counter IC3 is counter IC2 produces a 608 kHz clock signal as well as a 19 kHz addition and subtraction control signal, but six phase reverser IC1 serves as the crystal oscillator and the buffer.
This basic electric circuit may perform to expand, the method is increases a resistance network, a multi-channel multiplexer and a reversible counter again. Exterior audio frequency source available L and the R tonic train signaling actuates the resistance network separately the upper extreme and the lower extremity. L and the R signal must pass through the low-pass filtering, filters is higher than 15 kHz the frequency components. A 1.216 MHz signal provides the clock signal for the second reversible counter, from the high frequency takes out a 38 kHz addition and subtraction control signal to meet to counter IC2. Increases the electric circuit produces the baseband L R channel, as well as with 19 kHz pilot frequency sound synchronization L-R modulation signal, because all clock pulse comes from a public counter. In order to produce the compound multiplexing signal, two simulation multi-channel multiplexer’s outputs add together in an exterior network.
Stipulates in the part situation in the use chart, this electric circuit has a 19 kHz pilot frequency sound, its overtone is 60db, is lower than the fundamental wave, and with 38 kHz carrier maximum value synchronization which suppresses. The identical circuit structure in does not change the part parameter value in the situation to be possible to provide the L R channel and the L-R channel. Potentiometer P1 may realize 90±10° precise phasing, with the aim of correcting distorts, realizes a zero crossing again synchronization.
