SL1452NADP Zarlink Semiconductor Inc, SL1452NADP Datasheet - Page 4

• Manufacturer Part Number: SL1452NADP
• Description: WIDEBAND LINEAR FM DETECTOR FOR SATELLITE TV
• Manufacturer: Zarlink Semiconductor Inc

SL1452 QUADRATURE DEMODULATOR
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.
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 0.1 F minimum but the input coupling and decoupling
values can be smaller, about 330pF being adequate.
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.
which is a quarter of the input frequency on pin 8 due to the two
internal 42 stages (see Fig.2).
frequency using:
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.
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.
The SL1452 FM demodulator has a simple application with
A good layout can usually be ensured by the simple precau-
The only remaining components to be selected are those
First determine the quadrature circuit operating frequency,
Choose suitable values for L and C to resonate at the correct
Once suitable L and C values have been determined, the
f =
2p=LC
OUTPUT
612MHz
VIDEO
INPUT
1
1n
0·1
15V
Fig. 4 Typical application
1n
5
6
7
8
SL1452
Q can be calculated from:
The internal 800
allowed for when calculating R.
Example
with centre frequency 480 MHz and video bandwidth of 10MHz.
Allowing for the internal 800 resistance between pins 2 and 3
(see Fig.3), the external resistance required is 234 . ; choose
270 .
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
270 obtained in the example is low enough to allow adequate
control.
will usually be necessary to make either the L or C a variable
component, the value being adjusted to obtain best linearity.
4
3
2
1
A value for total damping resistor value to obtain the required
Design a quadrature circuit to demodulate a carrier on pin 8
It should be remembered that the internal 800 resistance is
In order to overcome the effects of component tolerances, it
For L = 40nH, f
C = 43·98pF (nearest preferred value 47pF)
From Table 1, Q required is approximately 6,
therefore total R required is:
0V
330
R = Q2 fL
= 6323 3480310
=181 ohms
10
Q
6
4
resistance between pins 2 and 3 must be
0·04
QUAD
R = Q2 fL
Table 1
= 120MHz,
4
27p
Bandwidth
7·5MHz
14MHz
23MHz
6
30·04310
26
3