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.