MC74HC4046A

The MC74HC4046A is similar in function to the MC14046 Metal gate CMOS device. The device inputs are compatible with standard CMOS outputs; with pullup resistors, they are compatible with LSTTL outputs.

The HC4046A phaselocked loop contains three phase comparators of MC74HC4046A, a voltagecontrolled oscillator (VCO) and unity gainopamp DEM_OUT. The comparators have two common signal inputs, COMP_IN, and SIG_IN. Input SIG_IN and COMP_IN can be used directly coupled to large voltage signals, or indirectly coupled (with a series capacitor to small voltage signals). The selfbias circuit adjusts small voltage signals in the linear region of the amplifier. Phase comparator 1 (an exclusive OR gate) provides a digital error signal PC1_OUT and maintains 90 degrees phase shift at the center frequency between SIG_IN and COMP_IN signals (both at 50% duty cycle). Phase comparator 2 (with leadingedge sensing logic) provides digital error signals PC2_OUT and PCP_OUT and maintains a 0 degree phase shift between SIG_IN and COMP_IN signals (duty cycle is immaterial). Thelinear VCO produces an output signal VCO_OUT whose frequency is determined by the voltage of input VCO_IN signal and the capacitor and resistors connected to pins C1A, C1B, R1 and R2. The unity gainopamp output DEM_OUT with an external resistor is used where the VCO_IN signal is needed but no loading can be tolerated. The inhibit input, when high, disables the VCO and all opamps to minimize standby power consumption.

Applications of MC74HC4046A include FM and FSK modulation and demodulation, frequency synthesis and multiplication, frequency discrimination, tone decoding, data synchronization and conditioning, voltagetofrequency conversion and motor speed control.