TDA4470

Rev. A4, 23-Feb-01

1 (17)

Multistandard Video-IF + Quasi Parallel Sound Processing

Description

The TDA4470 is an integrated bipolar circuit for multi-
standard video/sound IF (VIF/SIF) signal processing in
TV/VCR and multimedia applications. The circuit
processes all TV video IF signals with negative

modulation (e.g., B/G standard), positive modulation
(e.g., L standard) and the AM, FM/NICAM sound IF
signals.

Features

D 5 V supply voltage; low power consumption
D Active carrier generation by FPLL principle

(frequency-phase-locked-loop) for true
synchronous demodulation

D Very linear video demodulation, good pulse response

and excellent intermodulation figures

D VCO circuit operates at picture carrier frequency, the

VCO frequency is switchable for L'-mode

D Alignment-free AFC without external reference

circuit, polarity of the AFC curve is switchable

D VIF-AGC for negative modulated signals (peak sync.

detection) and for positive modulation (peak white/
black level detector)

D Tuner AGC with adjustable take over point
D Alignment-free quasi parallel sound (QPS) mixer for

FM/NICAM sound IF signals

D Intercarrier output signal is gain controlled (necessary

for digital sound processing)

D Complete alignment-free AM demodulator with gain

controlled AF output

D Separate SIF-AGC with average detection
D Two independent SIF inputs
D Parallel operation of the AM demodulator and QPS

mixer (for NICAM-L stereo sound)

D Package and relevant pinning is compatible with the

single standard version TDA4472, which simplifies
the design of an universal IF module

Package: SDIP28, SO28, SSO28

Ordering Information

Extended Type Number

Package

Remarks

TDA4470-MSD

SDIP28

TDA4470-MFLG3

SO28

Delivery in taped form

TDA4470-MFS

SSO28

Delivery in tubes

TDA4470-MFSG3

SSO28

Delivery in taped form

TDA4470

Rev. A4, 23-Feb-01

3 (17)

Circuit Description

Vision IF Amplifier

The video IF signal (VIF) is fed through a SAW filter to
the differential input (Pin 6-7) of the VIF amplifier. This
amplifier consists of three AC-coupled amplifier stages.
Each differential amplifier is gain controlled by the auto-
matic gain control (VIF-AGC). The output signal of the
VIF amplifier is applied to the FPLL carrier generation
and the video demodulator.

Tuner-and VIF-AGC

At Pin 8, the VIF-AGC charges/discharges the AGC
capacitor to generate a control voltage for setting the gain
of the VIF amplifier and tuner in order to keep the video
output signal at a constant level. Therefore, in the case of
all negative modulated signals (e.g., B/G standard) the
sync. level of the demodulated video signal is the
criterion for a fast charge/discharge of the AGC capacitor.
For positive modulation (e.g., L standard) the peak white
level of video signal controls the charge current. In order
to reduce reaction time for positive modulation, where a
large time constant is needed, an additional black level
detector controls the discharge current in the event of
decreasing VIF input signal. The control voltage (AGC
voltage at Pin 8) is transferred to an internal control
signal, and is fed to the tuner AGC to generate the tuner
AGC current at Pin 11 (open collector output). The take
over point of the tuner AGC can be adjusted at Pin 10 by
a potentiometer or an external dc voltage (from interface
circuit or microprocessor).

FPLL, VCO and AFC

The FPLL circuit (frequency phase locked loop) consists
of a frequency and phase detector to generate the control
voltage for the VCO tuning. In the locked mode, the VCO
is controlled by the phase detector and in unlocked mode,
the frequency detector is superimposed. The VCO
operates with an external resonance circuit (L and C par-
allel) and is controlled by internal varicaps. The VCO
control voltage is also converted to a current and repre-
sents the AFC output signal at Pin 22. At the AFC switch
(Pin 19) three operating conditions of the AFC are pos-
sible: AFC curve "rising" or "falling" and AFC "off".

A practicable VCO alignment of the external coil is the
adjustment to zero AFC output current at Pin 22. At center
frequency the AFC output current is equal to zero.
Furthermore, at Pin 14, the VCO center frequency can be
switched for setting to the required L' value (L' standard).

The optional potentiometer at Pin 26 allows an offset
compensation of the VCO phase for improved sound
quality (fine adjustment). Without a potentiometer (open
circuit at Pin 26), this offset compensation is not active.

The oscillator signal passes a phase shifter and supplies
the in-phase signal (0

╟

) and the quadrature signal (90

╟

)of

the generated picture carrier.

Video Demodulation and Amplifier

The video IF signal, which is applied from the gain
controlled IF amplifier, is multiplied with the inphase
component of the VCO signal. The video demodulator is
designed for low distortion and large bandwidth. The
demodulator output signal passes an integrated low pass
filter for attenuation of the residual vision carrier and is
fed to the video amplifier. The video amplifier is realized
by an operational amplifier with internal feedback and
8 MHz bandwidth (ґ3 dB). A standard dependent dc level
shift in this stage delivers the same sync. level for positive
and negative modulation. An additional noise clipping is
provided. The video signal is fed to VIF-AGC and to the
video output buffer. This amplifier with a 6 dB gain offers
easy adaption of the sound trap. For nominal video IF
modulation the video output signal at Pin 12 is 2 V

pp.

Sound IF Amplifier and SIF-AGC

The SIF amplifier is nearly identical with the 3-stage VIF
amplifier. Only the first amplifier stage exists twice and
is switchable by a control voltage at Pin 3. Therefore with
a minimal external expense it is possible to switch
between two different SAW filters. Both SIF inputs
features excellent cross-talk attenuation and an input
impedance which is independent from the switching
condition.

The SIF-AGC is related to the average level of AM- or
FM-carrier and controls the SIF amplifier to provide a
constant SIF signal to the AM demodulator and QPS
mixer.

AM Demodulator

The alignment-free AM demodulator is realized by a
synchronous detector. The modulated SIF signal from the
SIF amplifier output is multiplied in phase with the
limited SIF signal (AM is removed). The AF signal of the
demodulator output is fed to the output amplifier and to
the SIF-AGC. For all TV standards with negative video
modulation (e.g., B/G standard), the AF output signal
(Pin 25) is switched off by the standard switch.

Quasi-Parallel-Sound (QPS) Mixer

The QPS mixer is realized by a multiplier. The SIF signal
(FM or NICAM carrier) is converted to the intercarrier
frequency by the regenerated picture carrier (quadrature
signal) which is provided from the VCO. The intercarrier
signal is fed via an output amplifier to Pin 24.

TDA4470

Rev. A4, 23-Feb-01

4 (17)

Standard Switch

To have equal polarity of the video output signal the
polarity can be switched in the demodulation stage in
accordance with the TV standard. Additional a standard
dependent dc level shift in the video amplifier delivers the
same sync. level. In parallel to this, the correct VIF-AGC
is selected for positive or negative modulated VIF signals.
In the case of negative modulation (e.g., B/G standard)
the AM output signal is switched off. For positive modu-
lation (L standard) the AM demodulator and QPS mixer
is active. This condition allows a parallel operation of the
AM sound signal and the NICAM-L stereo sound.

L' Switch

With a control voltage at Pin 14 the VCO frequency can
be switched for setting to the required L' value (L'
standard). Also a fine adjustment of the L'-VCO center
frequency is possible via a potentiometer. The L' switch
is only active for positive modulated video IF-signals
(standard switch in L mode).

AFC Switch

The AFC output signal at Pin 22 can be controlled by a
switching voltage at Pin 19. It is possible to select an AFC
output signal with a rising- or falling AFC curve and to
switch off the AFC.

VCR Mode

For the VCR mode in a TV set (external video source
selected), it is recommendable to switch off the IF circuit.
With an external switching voltage at Pin 6 or 7, the IF
amplifiers are switched off and all signal output levels at
Pins 12, 24, and 25 are according to the internal dc
voltage.

Internal Voltage Stabilizer

The internal bandgap reference ensures constant perfor-
mance independent of supply voltage and temperature.

TDA4470

Rev. A4, 23-Feb-01

5 (17)

Pin Description

i,SIF1

GND

AGC

i,SIF1

i,VIF

AGC

GND

top

tun

o,vid

i,SIF2

comp

o,AM

o,FM

AFC

VCO

Ref

GND

94 8680

Figure 2. Pinning

Symbol

Function

1, 2

SIF1

SIF1 input (symmetrical)

Input selector switch

4, 9, 16

GND

Ground

AGC

SIF-AGC (time constant)

6, 7

i, VIF

VIF input (symmetrical)

AGC

VIF-AGC (time constant)

top

Take over point, tuner AGC

tun

Tuner AGC output current

o,vid

Video output

Standard switch

L' switch

Black level capacitor

ref

Internal reference voltage

Loop filter

AFC switch

20, 21

VCO

VCO circuit

AFC

AFC output

Supply voltage

Intercarrier output

O, AM

AF output ґ AM sound

comp

Offset compensation

27, 28

i, SIF2

SIF 2 input (symmetrical)

Part Number TDA4470