ADVANCE INFORMATION
2029-2·1
SL1452
WIDEBAND LINEAR FM DETECTOR FOR SATELLITE TV
With a minimum of external components, the SL1452 forms a
complete wideband FM detector suitable for use in satellite TV.
The video output and bandwidth may be optimised by adjustment
of the working Q of the quadrature coil.
FEATURES
s
High Operating Frequency Simplifies Image Filtering
0V
DEMODULATOR COIL
DEMODULATOR COIL
0V
1
2
8
7
INPUT SIGNAL
INPUT REF
V
CC
VIDEO OUTPUT
s
Negligible Differential Gain and Phase Errors
s
Video Bandwidth Suitable for High Definition TV
s
High Sensitivity and Wide Dynamic Range
s
Wide Operating Frequency Range: 300 to 1000 MHz
s
Electrostatic Protection
*
*
Normal ESD handling precautions should be observed
ORDERING INFORMATION
SL1452 NA DP
(8-lead plastic DIL package)
SL1452 NA MP
(8-lead miniature plastic DIL package)
SL1452
3
4
6
5
DP8
0V
DEMODULATOR COIL
DEMODULATOR COIL
0V
1
2
8
7
INPUT SIGNAL
INPUT REF
V
CC
VIDEO OUTPUT
SL1452
3
4
6
5
ABSOLUTE MAXIMUM RATINGS
Operating temperature range
Supply voltage, pin 6
Input voltage, pin 7 or 8
Storage temperature
Junction temperature
210°C
to180°C
7V
2·5V p-p
255°C
to
1150°C
1175°C
MP8
Fig. 1 Pin connections - top view (not to scale)
QUADRATURE
DEMODULATOR
COMPONENTS
1k
2k
70p
1k
INPUT REF
INPUT SIGNAL
7
8
2
3
V
CC
6
2k
2p
2p
44
5
VIDEO OUTPUT
INPUT
AMPLIFIER
DEMODULATOR
VIDEO
AMPLIFIER
1
4
0V
0V
Fig. 2 Block diagram
SL1452
ELECTRICAL CHARACTERISTICS
These characteristics are guaranteed over the following conditions (unless otherwise stated):
T
AMB
=
125°C,
V
CC
=
14·5V
to
15·5V,
Q = 6, f = 612MHz
Characteristic
Pin
Min.
Supply current, I
CC
Video output voltage
Video bandwidth
Minimum operating frequency
Maximum operating frequency
Input voltage
Intermodulation
6
5
5
8
8
8
5
Value
Typ.
40
0·7
14
300
1000
10
260
Max.
50
mA
V p-p
MHz
MHz
MHz
mVrms
dB
V
CC
= 5V
Df
= 13·5MHz p-p
Units
Conditions
300
Differential gain
Differential phase
Signal-to-noise ratio
5
5
5
70
,61
,61
%
deg
dB
Product of input modulation: f = 4·4MHz,
Df
= 13·5MHz p-p and f = 6MHz,Df = 2MHz p-p
(PAL colour and sound subcarriers).
Df
= 13·5MHz p-p. Demodulated staircase
referred to input staircase before modulation.
Demodulated colour bar waveform referred to
waveform before modulation.
Ratio of output with
Df
= 13·5MHz p-p at 1MHz
to output rms noise in 10MHz bandwidth
with
Df
= 0.
QUADRATURE COIL
2
3
15V
15V
1·75k
5
3·2k
400
400
2mA
1·8k
2·5V
2p
0V
2k
0V
2·5V
2k
640
0V
VIDEO
OUTPUT
70p
1k
2mA
2p
0V
3mA
0V
1k
8
7
INPUT
SIGNAL
INPUT
REF
Fig. 3 Input/output interface circuits
2
SL1452
15V
VIDEO
OUTPUT
5
6
4
3
0·04µ
SL1452
1n
612MHz
INPUT
0·1µ
1n
7
8
2
1
330
27p
0V
Fig. 4 Typical application
SL1452 QUADRATURE DEMODULATOR
The SL1452 FM demodulator has a simple application with
very low external component count. This is demonstrated by the
applications circuit diagram Fig. 4, but as with most integrated
circuits, particularly those working at high frequencies, some
attention to good RF layout techniques and correct component
selection will ensure optimum results.
A good layout can usually be ensured by the simple precau-
tion of keeping all components close to the SL1452, maintaining
short lead lengths and ensuring a good low impedance ground
plane. Double sided board layout enables these objectives to be
easily met, but is not essential for satisfactory operation. All
coupling and decoupling capacitors should be chosen for low
impedance characteristics at high frequencies, multilayer ce-
ramic types usually providing small size and adequate high
frequency performance. For the quadrature coil tuning capacitor
a fairly stable component should be selected to prevent excessive
drift. The power supply decoupling capacitor from pin 6 to ground
should be 0.1µF minimum but the input coupling and decoupling
values can be smaller, about 330pF being adequate.
The only remaining components to be selected are those
forming the quadrature circuit on pins 2 and 3 and some care in
the determination of values for these is required if maximum
performance is to be obtained.
First determine the quadrature circuit operating frequency,
which is a quarter of the input frequency on pin 8 due to the two
internal
42
stages (see Fig.2).
Choose suitable values for L and C to resonate at the correct
frequency using:
1
2p=LC
The value of C should by greater than 15pF to prevent stray
capacitance effects introducing errors and distortion of the
demodulation curve, but the use of very large capacitances with
small inductance values will lower the impedance of the tuned
circuit at the required Q value, reducing the drive level to the
demodulator and thereby restricting the video output available.
In general, for operation in the 400MHz to 600MHz range, an
inductance value between 40nH and 60nH is recommended.
Once suitable L and C values have been determined, the
working Q for the quadrature circuit should be set, the Q value
determining the video output level and bandwidth. Video output
is proportional to Q whereas video bandwidth is inversely
proportional. The effect of Q variations on video bandwidth and
amplitude can be determined from Table 1 and the graphs in Fig. 5.
f=
A value for total damping resistor value to obtain the required
Q can be calculated from:
R = Q2πfL
The internal 800Ω resistance between pins 2 and 3 must be
allowed for when calculating R.
Example
Design a quadrature circuit to demodulate a carrier on pin 8
with centre frequency 480 MHz and video bandwidth of 10MHz.
For L = 40nH, f
QUAD
= 120MHz,
C = 43·98pF (nearest preferred value 47pF)
From Table 1, Q required is approximately 6,
therefore total R required is:
R = Q2πfL
= 6323π
3480310
6
30·04310
26
4
=181 ohms
Allowing for the internal 800Ω resistance between pins 2 and 3
(see Fig.3), the external resistance required is 234Ω ; choose
.
270Ω.
It should be remembered that the internal 800Ω resistance is
subject to production tolerances and if fairly close control of
video bandwidth is required, the L and C ratio may require some
adjustment to ensure that the external R is sufficiently low to
swamp the effect of internal resistance changes. The value of
270Ω obtained in the example is low enough to allow adequate
control.
In order to overcome the effects of component tolerances, it
will usually be necessary to make either the L or C a variable
component, the value being adjusted to obtain best linearity.
Q
10
6
4
Bandwidth
7·5MHz
14MHz
23MHz
Table 1
3
PCB Design
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