Video Modulator for
FM-Audio
TDA 5666-5
Preliminary Data
Features
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Bipolar IC
FM-audio modulator
Sync level clamping of video input signal
Controlling of peak white value
Continuous adjustment of modulation depth for
positive or negative values
Symmetrical mixer output with separate ground area
Symmetrical oscillator with separate RF-ground
Low spurious radiation
High stability of the RF-oscillator frequency
High stability of the audio oscillator
Internal reference voltage
12 V supply voltage
P-DIP-18 -5
Type
TDA 5666-5
Ordering Code
Q67000-A5168
Package
P-DIP-18-5
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.
Semiconductor Group
1
02.95
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
Ω
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 kΩ 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
Ω.
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.
Semiconductor Group
2
TDA 5666-5
Pin Configuration
(top view)
Semiconductor Group
3
TDA 5666-5
Pin Definitions and Functions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Symbol
FM-Audio
V
REF
OSC-Input 1
OSC-Out 1
OSC-Ground
OSC-Out 2
OSC-Input 2
V
S
N.C.
Video
Video-Capacitor
Modulation
Output 2
Ground
Output 1
Audio carrier ratio
FM-Audio OSC
FM-Audio OSC
Function
AF-input for FM-modulation
Internal reference voltage (7.5 V)
Symmetrical oscillator input
Symmetrical oscillator output
Oscillator ground
Symmetrical oscillator output
Symmetrical oscillator input
Supply voltage (12 V)
Not connected
Video input with clamping
Connection for smoothing capacitor for video control
loop
Switch-over for positive and negative modulation
Symmetrical RF-output
Ground
Symmetrical RF-output
Video to audio carrier ratio adjustment
FM-audio oscillator; symmetrical inputs for tank circuit
FM-audio oscillator; symmetrical inputs for tank circuit
Semiconductor Group
4
TDA 5666-5
Block Diagram
Semiconductor Group
5
