FM Stereo

AN7415 is a monolithic integrated circuit that can be used in FM stereo demodulation applications. The operating voltage range is 1.6 to 7Vdc. Two AA dry cells are enough for powering this IC and it makes the AN7415 suitable for handheld FM radio applications. AN7415 has low current consumption (2.6mA), low distortion, good channel separation and high gain. The IC is available in 16 pin DIL package.

Description.

The circuit shown below is of a PLL FM stereo demodulator designed based on the AN7415. C1 is the input coupling capacitor which blocks any DC voltage present in the multiplexed input signal. LED D1 is an indicator LED and R1 is its current limiting resistor. C4 and C5 are the DC decoupling capacitors for the left and right output channels. C2 and C3 are the noise bypass capacitors for the left and right output channels. POT R2 can be used for adjusting the channel separation. Resistor R5 and capacitors C7 and C8 forms a low-pass filter network for the internal DC amplifier circuitry (see the block diagram of AN7415). C10 is a filter capacitor for the IC’s internal Schmitt trigger amplifier circuitry. C9 is a ripple filter capacitor for the voltage stabilizer circuit inside the AN7415. Resistor R3, POT R4 and Capacitor C6 sets the time constant of the internal VCO circuit. Hence POT R4 can be used for adjusting the VCO frequency. A 19KHz frequency check signal is available at the PIN 12 of the IC. Switch S1 can be used for enabling and disabling forced mono function.

Circuit diagram.

AN7415 stereo decoder

Notes.

• Well designed and good quality PCB improves the performance.
• Input supply voltage range is from 1.6V to 7VDC.
• I recommend 3VDC for powering the circuit.
• POT R4 can be used for adjusting the voltage controlled oscillator (VCO) frequency.
• POT R2 can be used for setting the channel separation.
• Recommended LED indicator current is 40mA.
• Maximum power dissipation is 80mW.