U4468B-MG Atmel, U4468B-MG Datasheet - Page 2

• Manufacturer Part Number: U4468B-MG
• Description: IC SOUND CIRC/AM DEMOD 16DIP
• Manufacturer: Atmel
• Type: Demodulatorr

Specifications of U4468B-MG

• Applications: Processing, IF Modules
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

2. Circuit Description
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2
IF Amplifier and AGC
Standard Switch
Internal Voltage Stabilizer
FPLL, VCO
AM Demodulator
Quasi-Split-Sound (QSS) Mixer
Mute Switch
U4468B
The symmetrical IF input signal from the external SAW filter is fed to the pins 1 and 2. In case of
FM/NICAM applications, a SAW filter with double band-pass characteristic is required for the
vision and sound carrier. In case of the L-standard, a band-pass filter with the center frequency
at the L-sound carrier is used.
The amplifier consists of three AC-coupled wide-band IF stages. Each differential amplifier stage
is gain controlled by the AGC (Automatic Gain Control) voltage, available at pin 3. The output
signal of the IF amplifier is then applied to the FPLL carrier generation, to the mixer for
FM/NICAM signals and to the AM demodulator.
The IF-AGC is derived from the average level of the AM carrier (L-standard) or from the peak
value of the FM carrier (e.g., B/G standard). It controls the three-stage wide-band amplifier to
provide a constant SIF signal to the AM demodulator or to the QSS (quasi-split sound) mixer.
If the standard switch (pin 7) is in position “low” (for AM sound), the AGC is operating as an aver-
age level detector. In position “open” or “high” (for FM/NICAM sound), the AGC acts as a peak
value detector.
The internal band gap reference voltage (4.25V at pin 4) ensures constant performance, inde-
pendent of supply voltage and temperature.
The FPLL (frequency-phase-locked loop) circuit consists of a frequency detector and a phase
detector to generate a control voltage for the VCO tuning. In locked mode, the VCO is controlled
by the phase detector while in unlocked mode, the frequency detector is superimposed. The
VCO operates with an external resonance circuit (L and C parallel) and is controlled by inte-
grated varicaps.
A practicable VCO alignment of the external coil is the adjustment of the loop filter voltage (pin
5) to 2.3 V. At this value, the capture and hold range are centered.
The alignment-free AM demodulator is realized by a synchronous detector. The modulated IF
signal from the wide-band IF amplifier output is multiplied in phase with the limited SIF signal to
remove the AM. Then, the resulting AF signal of the demodulator output is fed to the output
amplifier and to the AGC stage.
The QSS mixer is realized by a multiplier circuit. The IF signal (FM/NICAM) is converted to the
intercarrier frequency by means of a quadrature signal from the generated picture carrier pro-
vided by the PLL. The intercarrier signal is fed via an output amplifier to pin 12.
The AM sound output (pin 6) can be muted by switching the pulling mute switch (pin 10) to “low”.
4777B–TVVCR–07/05