Video Modulator for
FM-Audio
Preliminary Data
Bipolar IC
TDA 5666-5
P-DIP-18 -5
Features
q
FM-audio modulator
q
Sync level clamping of video input signal
q
Controlling of peak white value
q
Continuous adjustment of modulation depth for
positive or negative values
q
Symmetrical mixer output with separate ground area
q
Symmetrical oscillator with separate RF-ground
q
Low spurious radiation
q
High stability of the RF-oscillator frequency
q
High stability of the audio oscillator
q
Internal reference voltage
q
12 V supply voltage
Semiconductor Group
1
02.95
Functional Description and Application
The monolitic integrated circuit TDA 5666-5 is especially suitable as a modulator for the
48- to 860-MHz frequency range.
Video recorders, cable converters, TV-converter networks, demodulators, video
generators, video security systems, amateur TV-applications and personal computers.
Type
Ordering Code
Package
TDA 5666-5
Q67000-A5168
P-DIP-18-5
Semiconductor Group
2
TDA 5666-5
Circuit Description
Oscillator
The RF-oscillator is available at pins 3-7. The oscillator operates as a symmetrical
Colpitts circuit. The oscillator chip ground, pin 5, should be connected to ground at the
resonance circuit shielding point. An external oscillator can be injected inductively or
capacitively via pins 3 and 7. The layout of the PCB should be such as to provide a
minimum shielding attenuation between the oscillator pins 3-7 and modulator output pins
13-15 of approximately 80 dB.
For optimal residual carrier suppression, the symmetrical mixer outputs at pins 13, 15
should be connected to a matched balanced-to-unbalanced broadband transformer, e.g.
a Guanella transformer with good phase precision at 0
o
and 180
o
. The transmission loss
should be less than 3 dB. In addition, an LC-low pass filter combination is required at the
output. The cut-off frequency of the low pass filter combination must exceed the
maximum operating frequency.
Video
The video signal with the negative synchronous level is capacitively connected to pin 10.
The internal clamping circuit is referenced to the synchronizing level. Should the video
signal change by 6 dB, this change will be compensated by the resonance circuit which
is set by the peak white value. At pin 11, the current pulses of the peak white detector are
filtered through the capacitor which also determines the control time constant. The RF-
carrier switches from negative to positive video modulation, when pin 12 is connected
to ground. By varying the value of resistance
R
at pin 12 between
... 0
the modulation
depth can be increased from 70% to 100% when the modulation is negative and
decreased from 100% to 70% when the modulation is positive.
Audio
Via pin 1, the audio signal is capacitively coupled to the AF-input for the FM-modulation
of the oscillator. A parallel resonance circuit is connected to the audio carrier oscillator at
pins 17, 18. The unloaded
Q
of the resonant circuit must be
Q
= 25 and the parallel
resistor
R
T
= 8.2 k
to ensure a video to audio carrier ratio of 12.5 dB. At the same time,
the capacitative and/or inductive reactance for the resonance frequency should have a
value of
X
C
X
L
800
.
The video to audio carrier ratio can be changed by connecting an external voltage to pin
16, which deviates from the internal reference voltage.
At the output of the above described mixer the FM modulated audio signal is added to
the video signal and mixed with the oscillator signal in the RF-mixer.
Source
The internal reference voltage is available at pin 2 and has to be capacitively blocked
there.
TDA 5666-5
Semiconductor Group
3
Pin Configuration
(top view)
Semiconductor Group
4
TDA 5666-5
Pin Definitions and Functions
Pin No.
Symbol
Function
1
FM-Audio
AF-input for FM-modulation
2
V
REF
Internal reference voltage (7.5 V)
3
OSC-Input 1
Symmetrical oscillator input
4
OSC-Out 1
Symmetrical oscillator output
5
OSC-Ground
Oscillator ground
6
OSC-Out 2
Symmetrical oscillator output
7
OSC-Input 2
Symmetrical oscillator input
8
V
S
Supply voltage (12 V)
9
N.C.
Not connected
10
Video
Video input with clamping
11
Video-Capacitor
Connection for smoothing capacitor for video control
loop
12
Modulation
Switch-over for positive and negative modulation
13
Output 2
Symmetrical RF-output
14
Ground
Ground
15
Output 1
Symmetrical RF-output
16
Audio carrier ratio
Video to audio carrier ratio adjustment
17
FM-Audio OSC
FM-audio oscillator; symmetrical inputs for tank circuit
18
FM-Audio OSC
FM-audio oscillator; symmetrical inputs for tank circuit
TDA 5666-5
Semiconductor Group
5
Block Diagram
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