PROJECT REPORT

ON
“FM RECEIVER”

DEPARTMENT
OF
ELECTRONIC AND COMMUNICATION ENGINEERING

JUN 2025
UNIVERSITY INSTITUTE OF ENGINEERING AND TECHNOLOGY
KUK ,KURUKSHETRA

Submitted To: Submitted By:

DR. Monish Harsh
Gupta Ansh
Asst.Professor B.Tech.(ECE)
Department of 8th Sem
ECE UIET KUK Roll no. -252101072
252101073
 ACKNOWLEDGEMENT

At the outset, I find it my obligation to thank the Almighty God for giving us necessary
wisdom to accomplish this project. I express my sincere thanks with high esteem and
gratitude to DR. Monish Gupta (Assistant Professor) (Department of Electronics
and Communication Engineering) for their timely help and allowing me to utilize the
facilities in the UIET KUK for the successful completion of this work.

Submitted By:
Harsh
Ansh
ECE-A 8th Semester
252101072
252101073
 DECLARATION

I hereby declare that the project work entitled “FM RECEIVER” submitted to the
University Institute of Engineering and Technology, Kurukshetra University,
Kurukshetra is a project done by me under the guidance of DR. Monish Gupta (Assistant
Professor) (Department of Electronics and Communication Engineering) and this
project work is submitted for the award of the degree Bachelor of Technology in
Electronics and Communication Engineering.

Submitted By:
Harsh
Ansh
ECE-A 8th Semester
252101072
252101073
 Project Stage-I

PROJECT MADE: FM RECIEVER

INTRODUCTION:An FM receiver is an electronic device that picks up radio waves modulated by frequency
variations (FM signals), decodes the audio information embedded within those variations, and then
produces a sound output.

LIST OF COMPONENTS:

1. Transformer: A 6-0-6, 250 mA transformer steps down the AC mains voltage to 12V (center-tapped for
symmetrical output). Provides dual 6V outputs for powering the circuit.
2. IN4007 diode: Two IN4007 diodes are configured in a full-wave rectifier setup, which converts AC to
pulsating DC.
3. 1000 µF electrolytic capacitor: A 1000 µF capacitor smoothens the DC voltage by filtering out ripples.
4. 5mm LED: Indicating whether the circuit is on or off.
5. SONY CXA 1619 IC: The Sony CXA1619 is an integrated circuit designed for FM/AM radio applications.
It combines RF amplification, intermediate frequency (IF) conversion, FM/AM demodulation, and
audio amplification into a single package. The IC simplifies the design of radio receivers by minimizing
external components, offering stable tuning, and providing high-quality audio output.
6. FM GANG CAPACITOR: In FM receivers, a 0-180pF gang capacitor tunes the RF amplifier and local
oscillator for optimal signal reception within the FM broadcast band.
7. VOLUME CONTROL: A 10k volume control is a potentiometer (variable resistor) commonly used in
audio circuits. It provides smooth adjustment of sound levels.
8. SPEAKER: A speaker is an electroacoustic transducer that converts electrical signals into sound waves.
A 4 ohm speaker is a type of loudspeaker with an electrical impedance of 4 ohms. This means it resists
the flow of electrical current with a value of 4 ohms.

LIST OF COMPONENTS USED IN THE APPLICATION CIRCUIT OF CXA1619 IC:

SONY CXA 1619 IC: The Sony CXA1619 is a single-chip integrated circuit (IC) designed for FM/AM radio
receivers.
• AF Power Amp: This is likely the audio power amplifier stage, responsible for boosting the audio
signal before it's sent to the speaker.
• AM IF DET AGC: This block likely handles the intermediate frequency (IF) signal for AM reception,
including detection and automatic gain control (AGC).
• FM IF: This block likely handles the IF signal for FM reception.
• FM Discriminator: This block is responsible for demodulating the FM signal to recover the audio.
• FM FE: This likely refers to the FM front-end, responsible for initial signal processing of the FM
input.
• Tuning Meter: This block likely drives the meter that indicates the strength of the received signal.
• AM FE: selecting the desired AM signal by filtering out unwanted frequencies and amplifying the
weak signal to a level suitable for subsequent stages. This combination of selectivity and
 sensitivity ensures that the receiver can effectively pick out the desired AM broadcast and process it
for clear and strong audio output.

SPECIFICATIONS OF SONY CXA 1619 IC:

Components in the circuit associated with SONY CXA1619 IC:
1. Capacitors: C1: 2 pF, C2: 18 pF, C3: 22 pF, C4: 6 pF, C5: 10 µf, C6 : 0.01 µf, C7 : 1 pf, C8: 4.7 µF, C10: 0.01
µF, C11: 100 pF, C12: 10 µF, 50V, C13: 10 µF, 50V, C14: 4.7 µF, 50V, C15: 0.47 µF, 50V, C16: 0.022 µF, C17:
10 µF, 50V, C18: 470 µF, 6.3V, C19: 0.1 µF, C20: 0.1 µF, C21: 220 µF, 10V.
2. Resistors: R1: 100 kΩ, R2: 10 kΩ, R3: 150 Ω, R4: 2.2 kΩ, R5: 330 Ω, R6: 1 kΩ, R7.
3. Inductors: L1, L2, L3, L4.
4. Diode: D1: Standard diode
5. Ceramic Filters: CF1: Ceramic filter CF2: Ceramic filter.

FM MODULATION: Frequency modulation consists of varying the frequency of the carrier voltage in
accordance with the instantaneous value of the modulating voltage. Thus the amplitude of the carrier does
not change due to frequency modulation. This is an advantage since any incidental disturbance such as
atmospheric disturbance or man made Static primarily appears in the form of variations of amplitude of the
carrier voltage and may be eliminated in a frequency modulation receiver which is made insensitive to
amplitude variation.

Working of an FM RECIEVER: An FM receiver works by converting incoming RF signals to a fixed

intermediate frequency (IF) for easier processing. The RF signal is amplified, mixed with a local oscillator
frequency, and the resulting IF signal is amplified and filtered for selectivity. The IF signal is then
demodulated to extract the original audio or data signal, which is amplified and sent to the output. This
design improves sensitivity, selectivity, and stability, making it ideal for AM/FM radios and communication
systems.

i. RF AMPLIFIER:
• The RF amplifier in a superheterodyne receiver is responsible for amplifying the weak radio frequency
(RF) signals received by the antenna before they are passed to the mixer.
• It enhances the sensitivity of the receiver, allowing it to detect faint signals, and improves selectivity by
filtering unwanted out-of-band signals.
• The RF amplifier is typically paired with a tuning circuit, such as an LC resonant circuit, which selects the
desired frequency band from the incoming signals.
• This allows the user to tune to a specific station.
• The amplifier boosts the strength of the selected RF signal using transistors or other active
components, ensuring the gain is sufficient without causing overloading or distortion.
• The amplified signal is then sent to the mixer stage, where it combines with the local oscillator's
frequency to produce an intermediate frequency (IF) for further processing.
• Key considerations in the design of the RF amplifier include bandwidth matching, high gain without self-
oscillation, low noise figure to maintain signal quality, and linearity to handle strong and weak signals
simultaneously.
• In the superheterodyne receiver, the RF amplifier significantly reduces noise, increases the range of
signal reception, and enhances the overall performance by preparing the signal for the next stages of
processing while maintaining its quality and integrity.

ii. FREQUENCY MIXER:

• The frequency mixer, a crucial component in a superheterodyne receiver, is responsible for converting
the received signal frequency to an intermediate frequency (IF) for easier processing.
• It achieves this by combining the incoming radio frequency (RF) signal with the frequency generated by a
local oscillator (LO).
• The mixer produces an output containing the sum and difference of these frequencies, with the desired
intermediate frequency being the difference between the LO and RF frequencies.
• This IF is constant regardless of the incoming signal's carrier frequency, enabling the use of fixed-
frequency amplification and filtering for better signal selectivity and noise rejection.
• Mixers can be implemented using diodes, transistors, or ICs, with their performance characterized by
factors like conversion gain, linearity, and noise figure.

iii. Local Oscillator:

• The local oscillator (LO) is a critical component in a superheterodyne receiver that generates a stable
sinusoidal signal at a specific frequency.
• Its primary function is to produce a frequency that, when mixed with the incoming radio frequency (RF)
signal, creates an intermediate frequency (IF).
• The LO operates in tandem with the frequency mixer, ensuring that the IF remains constant regardless
of the tuning frequency of the incoming signal.
• This constancy simplifies subsequent signal processing, such as amplification and filtering, by allowing
the use of fixed-frequency components.
• The LO's frequency is adjustable and is controlled to be offset by a fixed value (typically the IF) from the
desired RF signal frequency.
• The stability and accuracy of the LO are vital for the receiver’s overall performance, as any drift or
instability can lead to poor signal selectivity and distortion.
• LOs can be implemented using various methods, including LC circuits, crystal oscillators, or modern
phase-locked loops (PLLs), depending on the desired stability and tuning range.

iv. IF Amplifier:
• Intermediate frequency (IF) is the fixed frequency to which a received radio frequency (RF) signal is
converted to facilitate easier processing in a superheterodyne receiver.
• The conversion is achieved through mixing the RF signal with a signal from the local oscillator (LO) in a
frequency mixer.
• The mixer outputs two main frequency components: the sum (fRF + fLO) and the difference ( fRF−fLO)
of the two input frequencies.
• The IF is chosen as the difference frequency: fIF = | fRF - fLO|.
• This constant IF simplifies filtering and amplification since the receiver can use fixed-frequency
components optimized for that frequency.
• The IF is typically chosen to balance good selectivity, image frequency rejection, and practical design
considerations. For FM radio, the standard IF is 10.7 MHz, and for AM radio, it is 455 kHz.

v. LIMITER:
• A limiter is a critical component in FM receivers, designed to improve the fidelity and reliability of
received signals by removing amplitude variations caused by noise and interference.
• FM signals inherently encode information in their frequency variations rather than amplitude, making
the amplitude irrelevant for demodulation.
• However, during transmission, amplitude variations may occur due to environmental factors such as
multipath propagation, fading, or interference.
• The limiter circuit processes the signal after amplification and before demodulation, clipping or limiting
the peaks of the amplitude to ensure a consistent signal level.
• The limiter ensures that the demodulator only processes the frequency information, effectively
suppressing amplitude noise and improving the signal-to-noise ratio.
• It accomplishes this by maintaining the output signal at a constant amplitude regardless of variations in
the input signal, as long as the input remains above a certain threshold.
• Typically implemented using active devices like transistors or operational amplifiers, limiters are
configured to operate in a non-linear region, where they "clip" excessive peaks.
• This clipping action creates a clean, constant-amplitude signal ideal for demodulation.
• In FM receivers, the limiter circuit works in tandem with the discriminator to ensure accurate signal
recovery, contributing to the overall robustness and high fidelity of FM transmission.

vi. FM DETECTOR (DISCRIMINATOR):

The Foster-Seeley discriminator is a widely used FM detector that demodulates frequency-modulated
signals by converting frequency variations into amplitude variations, which are then rectified to retrieve
the original baseband signal. This type of FM detector operates based on the principle of frequency-to-
voltage conversion using a phase-shift network and a balanced diode arrangement.

Working Principle:
• The Foster-Seeley discriminator relies on a tuned circuit that is centered at the intermediate
frequency (IF). The incoming FM signal is fed into this circuit, which splits the signal into two paths.
• Each path is processed through components that are sensitive to phase shifts caused by frequency
deviations in the FM signal.
• The circuit uses a pair of diodes connected to a center-tapped transformer in the phase-shift
network.
• When the input signal frequency matches the center frequency of the tuned circuit, the two diode
paths produce equal and opposite voltages, resulting in no output.
• However, when the input frequency deviates (either increases or decreases), the phase shift causes
an imbalance in the voltages generated by the two diode paths.
• This imbalance creates a voltage difference that is proportional to the frequency deviation,
representing the demodulated signal.

Circuit Components and Function:

• Transformer: The input signal passes through a center-tapped transformer, which splits the signal
into two balanced paths.
• Diodes: Two diodes rectify the signal in each path, generating voltages proportional to the frequency
deviation.
• Capacitors and Resistors: These components filter and smooth the output signal to ensure a clean
demodulated waveform.
 • Load Resistor: The final demodulated output voltage is taken across the load resistor.

Advantages:
• Linearity: The Foster-Seeley discriminator provides a good linear response for small frequency
deviations, making it ideal for FM signals.
• Simplicity: The circuit is straightforward to design and implement.
• High Fidelity: It preserves the quality of the demodulated signal.

Limitations:
• Noise Susceptibility: It can be affected by amplitude variations in the FM signal, which is why
limiters are often used before the discriminator.
• Tuning Sensitivity: The circuit must be precisely tuned to the IF frequency for optimal performance.
• Limited Bandwidth: It works best for signals with relatively small frequency deviations.
• In essence, the Foster-Seeley discriminator is a cornerstone of FM demodulation, translating
frequency variations into voltage changes that faithfully represent the original signal. It is a robust
and efficient method used in FM radios and other communication systems requiring frequency
demodulation.

vii. AF AMPLIFIER:
• The AF (Audio Frequency) Amplifier amplifies the weak audio signal received from the FM or AM
detector to a level suitable for driving output devices like speakers or headphones.
• It operates within the audio frequency range of 20 Hz to 20 kHz.
• The amplifier consists of stages for voltage amplification, which boosts the signal strength, and power
amplification, which increases the current or power to drive the output load effectively.
• Key components include transistors or integrated circuits for amplification, resistors for biasing,
capacitors for coupling and filtering, and sometimes transformers for impedance matching.
• The amplifier ensures minimal distortion, proper impedance matching, and effective noise reduction to
maintain signal quality.
• It is widely used in radios, communication devices, public address systems, and other audio-related
applications to deliver clear and loud sound output.

Working of the Circuit:

i. Centre Tapped Transformer ( 6-0-6, 250 mA ):

• A center-tapped transformer functions similarly to a standard transformer.

• The only difference is that its secondary winding is separated into two distinct parts, allowing for the
obtaining of two separate voltages across the two-line ends.
• The internal process is the same: when an alternating current is applied to the transformer’s primary
winding, it generates a magnetic flux in the core, and when the secondary winding is brought close, an
alternating magnetic flux is induced in the secondary winding as the flux flows via the ferromagnetic
iron core and changes direction with each cycle of the alternating current.
• In this method, an alternating current move through the two sides of the transformer’s secondary
winding and into the external circuit.
• It will produce 12 volts peak to peak and RMS voltage between any single tap and the center tap will
be 6V RMS and a current drain of 250 Ma

ii. FULL WAVE CENTRE TAPPED RECTIFIER CIRCUIT:

Construction of the rectifier circuit:

• Diodes D1 and D2 are arranged to form a full-wave rectifier. The 1N4007 diodes are commonly used for
rectification because they can handle moderate currents and voltages (up to 1A and 1000V).
• The anodes of the diodes are connected to the two ends of the secondary winding of the transformer
(6V ends).
• The cathodes of the diodes are connected together and provide the DC output, which is also
connected to the load and the capacitor.
• The diodes allow current to flow only during the appropriate half-cycles of the AC input, ensuring that
the output current flows in one direction through the load.
• 1000µF Capacitor: The capacitor is connected across the load and the cathodes of the diodes.
• Its purpose is to filter the rectified signal, converting the pulsating DC into a smoother, more constant
DC voltage.
• The 1000µF capacitor stores energy during the peaks of the AC waveform and discharges during the
non-conducting periods of the diodes, reducing ripple and maintaining a more stable voltage across the
load.

Working of the rectifier circuit:

Step 1: AC Input and Transformer Action

• AC Supply Input: The transformer is connected to an AC supply at its primary side.

• Voltage Reduction: The 6-0-6 step-down transformer reduces the AC voltage from the primary side to a
lower voltage on the secondary side. Here, the secondary side has two ends that each provide 6V RMS
relative to the center tap.
• Center Tap: The center tap acts as the reference point (0V) or ground for the circuit, and it divides the
secondary winding into two halves. Each side provides 6V RMS with respect to the center tap.
• Primary Voltage (AC): For example, if the input AC is 220V, the transformer steps it down to 6V RMS on
each side of the center tap (with a total of 12V RMS across the outer windings of the secondary).

Step 2: Diode Conduction in Full-Wave Rectifier

Positive Half-Cycle:

• Positive Half-Cycle of AC: When the AC input goes through the positive half-cycle, the voltage at the
upper side of the secondary winding becomes positive relative to the center tap.
• Diode D1 Conducts: This positive voltage forward-biases Diode D1 (the diode connected to the upper
side of the secondary), causing D1 to conduct. As a result, current flows through the load, then through
D1, and charges the capacitor.
• Capacitor Charging: The capacitor charges up to the peak voltage of the AC waveform, minus the voltage
drops across the diode (approximately 0.7V per diode).
 Negative Half-Cycle:

• Negative Half-Cycle of AC: During the negative half-cycle of the AC, the voltage at the lower side of the
secondary becomes positive relative to the center tap, and the upper side becomes negative.
• Diode D2 Conducts: This positive voltage forward-biases Diode D2 (the diode connected to the lower
side of the secondary), causing D2 to conduct and allow current to flow through the load in the same
direction as during the positive half-cycle. The current flows through D2, charging the capacitor again.
• Capacitor Charging: The capacitor gets charged to the peak voltage of the AC waveform during the
negative half-cycle as well.

Step 3: Voltage Across the Capacitor

• The 1000µF capacitor helps to smooth the pulsating DC. The capacitor charges up to the peak voltage
during each half-cycle of the AC and stores this charge.
• When the AC supply is in the non-conducting phase, the capacitor discharges slightly to maintain the
voltage, reducing the ripple in the output.
• The DC output voltage across the capacitor will be close to the peak AC voltage (minus the diode drops).
• For example, if the secondary voltage of the transformer is 6V RMS, the peak voltage would be around:

Considering the voltage drop across the two diodes (0.7V + 0.7V = 1.4V), the voltage across the capacitor
will be approximately:

Step 4: DC Output (Filtered)

• The voltage across the capacitor will be a pulsating DC, with the capacitor charging during each half-
cycle and holding its charge in between cycles.
• The 1000µF capacitor provides a smoothing effect, ensuring that the output voltage is relatively stable
and free from large fluctuations.
• The output voltage, therefore, will be DC, but with a small ripple, which depends on the capacitor's value
and the load current.

SONY CXA 1619 AND THE CIRCUIT ASSOCIATED WITH IT:

1. Antenna and the Band Pass Filter:

• A copper coiled antenna is used which consists of coiling the copper wire into a spiral or helical shape.
The coil increases the inductance of the antenna, making it more effective in receiving electromagnetic
waves.
• The primary function of the antenna is to receive electromagnetic waves. In FM radio, these waves carry
the modulated signals that encode sound information. The FM transmitter broadcasts signals at a certain
frequency (typically between 88 MHz and 108 MHz in most regions).
• The antenna captures these electromagnetic waves, converting them into an alternating current (AC)
signal that corresponds to the transmitted radio waves.
• The antenna is usually designed to be resonant at the frequency range of the FM signals. FM signals
typically have wavelengths between 3.41 meters (88 MHz) and 2.78 meters (108 MHz).The length of the
antenna is usually chosen to match these wavelengths for effective reception. In most cases, a half-wave
dipole antenna is used, which is about half the wavelength of the FM signals being received.
• Once the antenna captures the radio waves, it produces a weak AC signal that is transmitted to the
receiver’s tuner. This weak signal is at the same frequency as the FM transmission but requires
amplification and processing to recover the audio signal.
• The band-pass filter is a critical component in an FM receiver, serving to select and pass only the desired
signal (the specific FM radio station you want to listen to) while rejecting all other unwanted frequencies
(such as noise and interference). Here's how it works:
a) Frequency Selection:
FM stations are transmitted at specific frequencies (e.g., 92.5 MHz, 101.3 MHz). The band-pass filter is
designed to pass signals within a specific frequency range (the "pass band") and filter out signals
outside of this range.
The band-pass filter essentially ensures that the receiver only processes the FM signals within the
desired frequency band (88 MHz to 108 MHz for FM radio) and blocks any frequencies outside this range.
b) Filtering Out Unwanted Signals:
Adjacent Channel Interference: The band-pass filter helps to reject interference from nearby frequencies
that are not part of the FM radio station you want to listen to. For example, if you are tuning to 92.5
MHz, the filter ensures that signals from 93.5 MHz or other frequencies are rejected.
Noise Reduction: It helps to filter out random signals or noise (such as electrical interference or spurious
signals) that might be picked up by the antenna or generated by other parts of the receiver.
c) Narrow Band for FM:
The filter typically has a narrow bandwidth to focus precisely on the FM station's frequency and avoid
distortion from adjacent signals. This narrow band ensures that only the FM station's modulated signal
(with its frequency deviations) is passed through for demodulation.
d) Improved Signal Quality:
By filtering out signals outside the desired frequency range, the band-pass filter improves the signal-to-
noise ratio (SNR). This leads to clearer audio output with minimal distortion, as only the desired
frequency components are passed through to the demodulator.

2. RF AMPLIFIER:

• The RF amplifier in an FM receiver is responsible for amplifying the weak radio frequency signals received
by the antenna before they are processed further.
• It improves the sensitivity of the receiver, enabling it to pick up even weak FM signals clearly. The RF
amplifier also helps in rejecting unwanted signals and noise by amplifying only the signals within the
desired frequency band.
• The RF amplifier typically includes a resonant LC circuit, which is tuned to the FM frequency range (88–
108 MHz).
• This circuit ensures that the amplifier focuses on the desired frequency while filtering out signals outside
 this range.
• The amplified signal is then passed to the next stage of the receiver, such as the mixer or intermediate
frequency (IF) stage, for further processing.
• The RF amplifier plays a crucial role in ensuring a strong and clear signal for demodulation, resulting in
better audio quality and overall receiver performance.
• The FM RF IN pin connects to the antenna and band-pass filter (BPF), capturing the FM signal from the
desired frequency range (88–108 MHz) and filtering out unwanted frequencies. The FM RF pin connects
to the LC resonant circuit, which is tuned to the desired frequency, allowing the amplified and filtered RF
signal to pass for further processing within the receiver.

3. Local Oscillator:

• The local oscillator in an FM receiver generates a stable, adjustable frequency that mixes with the
incoming radio frequency (RF) signal in the mixer stage to produce a fixed intermediate frequency (IF),
typically 10.7 MHz.
• This process, called heterodyning, enables the receiver to convert high-frequency signals into a lower,
fixed frequency for easier processing.
• The local oscillator frequency is tuned in synchronization with the RF signal to ensure the desired
station always results in the same IF.
• This allows for efficient amplification, filtering, and demodulation of the FM signal, ensuring clear and
stable reception.
• This is done by FM OSC PIN (8) and this pin is connected to a resonating circuit and further the variable
capacitance of the resonant circuit is adjusted by FM GANG CAPACITOR.

4. FM GANG CAPACITOR ( 0 – 180pF) :

• A gang capacitor in an FM receiver is a variable capacitor with multiple sections, mechanically linked to
adjust all sections simultaneously. It is used to tune the receiver to a specific FM frequency by varying
the capacitance in the resonant circuits associated with both the RF amplifier (FM RF) and the local
oscillator (FM OSC).

• The gang capacitor connects to two critical resonant circuits:

FM RF Pin (Resonant Circuit for RF Stage): One section of the gang capacitor is part of the resonant
circuit connected to the FM RF pin. This circuit is responsible for selecting the desired radio frequency
(RF) signal from the antenna. By adjusting the gang capacitor, the resonant frequency of this circuit is
tuned to the carrier frequency of the desired FM station.
FM OSC Pin (Resonant Circuit for Local Oscillator): Another section of the gang capacitor is connected
to the resonant circuit at the FM OSC pin. This circuit determines the frequency of the local oscillator.
The local oscillator frequency is typically offset by the intermediate frequency (IF), commonly 10.7 MHz
in FM receivers, from the RF frequency.

• As the gang capacitor is adjusted, both resonant circuits are simultaneously tuned. This ensures that
the RF stage selects the desired FM signal, and the local oscillator generates the correct frequency to
mix with the RF signal, producing the IF signal for further processing. The synchronization of these two
resonant circuits is critical for accurate tuning and reception of FM signals without interference.
The gang capacitor's role is fundamental in the seamless tuning of FM receivers, enabling precise alignment
of the RF and oscillator circuits for optimal signal reception.

5. Frequency Mixer:

• The frequency mixer in an FM receiver is responsible for converting the high-frequency RF signal
received from the antenna into a lower, fixed intermediate frequency (IF) signal, typically 10.7 MHz.
• It achieves this by combining the RF signal with the signal generated by the local oscillator.
• During this process, the mixer produces two new frequencies: the sum and the difference of the RF and
oscillator frequencies.
• The circuit then filters out the sum frequency and retains the difference frequency (the IF).
• This conversion simplifies the signal processing and ensures that the subsequent filtering and
amplification stages operate at a consistent frequency, improving the selectivity and sensitivity of the
receiver.
• The mixer is an essential component, as it enables the receiver to tune to various stations while
maintaining consistent performance.

6. 3-PIN CERAMIC FILTER AS IF FILTER:

• After completion of process at FREQUENCY MIXER, the signal from FM FRONT END will go outside
through the FM/AM FE OUT PIN (15). From this onwards the IF SIGNAL will pass through the CERAMIC
FILTER which will act as INTERMEDIATE FREQUENCY FILTER.
• Ceramic Filter provides sharp frequency selectivity and stable performance for the intermediate
frequency (IF) signal, typically 10.7 MHz in FM receivers. Ceramic filters are used after the mixer to allow
only the desired IF signal to pass through while rejecting unwanted frequencies.
• The ceramic filter will then refine this IF signal to ensure that only the desired signal components pass
through for demodulation.

7. IF AMPLIFIR:

• The filtered IF SIGNAL will then enter through the FM IF IN (18) PIN and here a multistage IF amplifier is
used to provide large gain. Further this IF amplifier should be designed to have overall bandwidth of 150
kHz.
• Since the overall bandwidth decreases as the no of stages in cascade increases, it is necessary to design
individual stages to have correspondingly higher bandwidth than the overall bandwidth desired.
• Double tuned circuits may be used but it is preferred, particularly at higher frequencies in the UHF
range, to use stagger tuned single tuned circuit which are found to produce more gain bandwidth
product than the conventional double tuned circuits.

8. LIMITER: It limits the IF voltage to a predetermined level and thus removes all amplitude variations
which may be incidentally caused due to changes in the transmission path or by a man made static or
natural static.
9. FM DETECTOR (DISCRIMINATOR):

• The discriminator detects the variations in frequency of the FM signal. In FM, the information (audio) is
encoded as changes in frequency. The discriminator detects these frequency deviations and converts
them into voltage variations proportional to the audio signal.
• The CXA1619 IC uses a ratio detector or phase-locked loop (PLL) mechanism within its FM detector. The
ratio detector works by comparing the input FM signal with a reference signal to detect the frequency
deviation. The PLL is used to synchronize the frequency of the local oscillator with the incoming FM
signal, helping to lock the receiver's tuning to the transmitted signal.
• The output of the discriminator is a voltage that varies in proportion to the frequency variations of the
FM signal.
• The CXA1619 also includes an automatic frequency control (AFC) feature that ensures the receiver stays
properly tuned to the incoming FM signal. It helps compensate for any frequency drift in the receiver or
transmitted signal, maintaining a stable demodulation process.

10. AF POWER AMPLIFIER:

• The demodulated signal will enter through AF IN (24) POWER AMPLIFIER INPUT PIN.
• A 10k ohm variable resistor is connected to VOL (4) for electronic volume control.
• The AF (Audio Frequency) Power Amplifier in an FM receiver plays a crucial role in amplifying the audio
signal so that it can drive speakers and produce sound.
• After the FM signal is received, filtered, amplified, and demodulated into an audio signal, the AF power
amplifier boosts the weak audio signal to a sufficient level for output.
• It typically uses transistor-based amplification or operational amplifier circuits, often in a class AB
configuration, which balances power efficiency and sound quality.
• The amplifier also includes signal conditioning features like volume control and tone adjustment to
enhance the listening experience.
• In addition, the AF power amplifier uses a negative feedback loop to reduce distortion and ensure the
audio signal remains accurate.
• It requires a high-voltage power supply to provide enough current to drive the speakers at loud volumes.
• Once amplified, the audio signal is sent to the speakers, converting the electrical signal into sound waves.
The amplifier's output is matched to the impedance of the speakers (commonly 4, 8, or 16 ohms) for
optimal energy transfer and to prevent damage.
• The amplifier also minimizes distortion and noise, ensuring high-quality sound output, and includes
thermal management systems to dissipate heat and prevent overheating.
Circuit Diagram: