A high quality FM receiver circuit based
on CXA1019 IC is shown here. CXA1019 is a bipolar silicon monolithic
FM/AM radio receiver IC from Sony. Built in circuitries inside the
CXA1019 include RF amplifier, mixer, oscillator, IF amplifier,
quadrature detection circuit, tuning LED driver electronic volume
control, detector etc. FM section of the IC is only utilized in this
circuit. The IC can be powered from anything between 3 to 7V DC and can
drive an 8 ohm loudspeaker.
Circuit diagram.
FM receiver circuit CXA1019
Circuit description.
Inductors L1, L2 and capacitors C4, C6,
C7 forms the tank circuit for the ICs built in oscillator section. The
IF output available at pin 15 is grounded through resistor R1. C1 is the
AC bypass capacitor for R1. Capacitor C16 is meant for ripple
filtering. LED D1 is a tuning indicator. Output of the built-in detector
stage (pin24) is coupled to the input (pin 25) of the built in AF
amplifier stage through capacitor C19, POT R2 and capacitor C18. The POT
R2 can be used as a volume control because it controls the input given
to the audio amplifier stage. Capacitor C15 couples the audio output to
the speaker and C14 is a noise bypass capacitor. C5 is just a power
supply filter while C20 couples the antenna to the FM RF input (pin13)
of the IC. The FM intermediate frequency output available at pin 15 is
filtered using the 10MHz ceramic filter and applied to the FM
intermediate frequency input pin18. Capacitor C2 is used for bypassing
noise from the audio power amplifier section inside the IC. The output
of this power amplifier section is around 500mW. Capacitor C1 and
transformer T1 are related to the FM discriminator circuitry inside the
IC. Resistor R3 is the feedback capacitor for the AGC section.
Notes.
- Assemble the circuit on a good quality PCB.
- For L1, make 2.75 turns of 22 SWG enamelled copper wire on a 5mm diameter plastic former.
- For L2, make 3.75 turns of 22 SWG enamelled copper wire on a 5mm plastic former.
- T1 is a FM IF transformer.
- CF1 is a 10.7MHz FM ceramic filter
- C4 is a 30pF dual gang FM tuning capacitor.
- The circuit can be powered from anything between 3V to 7V DC.
- Using a battery for powering the circuit will reduce noise and improve the performance
- If you using a battery eliminator, then it must be well regulated and free from noise.
- K1 can be a 3W, 8 ohm loudspeaker.
- A1 can be a 100cm long whip antenna.