SL1461SA
Wideband PLL FM Demodulator
Advance Information
The SL1461SA is a wideband PLL FM demodulator,
intended primarily for application in satellite tuners.
The device contains all elements necessary, with the
exception of external oscillator sustaining network and loop
feedback components, to form a complete PLL system
operating at frequencies up to 800MHz.
An AFC with window adjust is provided, whose output
signal can be used to correct for any frequency drift at the head
end local oscillator.
DS4358
ISSUE 1.3
September 1999
Ordering Information
SL1461SA/KG/MPAS
FEATURES
I
Single chip PLL system for wideband FM
demodulation
I
Simple low component count application
I
Allows for application of threshold extension
I
Fully balanced low radiation design
I
High operating input sensivity
I
Improved VCO stability with variations in supply or
temperature
I
AGC detect and bias adjust
I
75Ω video output drive with low distortion levels
I
Dynamic self biasing analog AFC
I
Full ESD Protection*
* Normal ESD handling procedures should be observed
AFC PUMP
AFC WINDOW ADJUST
V
EE
OSCILLATOR +
OSCILLATOR –
AGC BIAS
AGC OUTPUT
RF INPUT
1
2
3
4
5
6
7
8
16
15
AFC OUTPUT
V
CC
VIDEO FEEDBACK +
VIDEO –
VIDEO +
VIDEO FEEDBACK –
VIDEO OUTPUT
RF INPUT
SL1461SA
14
13
12
11
10
9
MP16
Fig.1 Pin connections - top view
APPLICATIONS
I
Satellite receiver systems
I
Data communications Systems
AGC BIAS
RF INPUTS
AGC OUTPUT
6
8
9
7
14
12
13
11
VIDEO
FEEDBACK +
VIDEO +
VIDEO –
VIDEO
FEEDBACK –
VIDEO
OUTPUT
AFC PUMP
AFC OUTPUT
10
1
LOCAL
OSCILLATOR
AFC WINDOW
ADJUST
4
5
16
2
Fig.2 SL1461SA block diagram
SP1461SA
Advance Information
ELECTRICAL CHARACTERISTICS
T
amb
= -20°C to +80°C, V
CC
= +4.5V to +5.5V. The electrical characteristics are guaranteed by either production test or design.
They apply within the specified ambient temperature and supply voltage unless otherwise stated.
Characteristics
Min.
Supply current
Operating frequency
Input sensitivity
Input overload
VCO sensitivity (dF/dV)
VCO linearity
VCO supply stability
VCO temperature stability
Phase detector gain
Loop amplifier input impedance
Loop amplifier output impedance
Loop amplifier open loop gain
Loop amplifier gain bandwidth product
Loop amplifier output swing
Video drive output impedance
Video drive:
Luminance nonlinearity
- differential gain
- differential phase
- intermodulation
- signal/noise
- Tilt
- baseline distortion
AGC output current
AGC bias current
AFC window current
AFC charge pump current
AFC leakage current
AFC output saturation voltage
10
0
0
50
10
0.4
66
72
0.3
0.4
3
2
400
250
400
1.9
0.5
1.0
5
2.5
3
-40
%
%
Degree
dB
dB
%
%
µA
µA
µA
µA
µA
V
With charge pump disabled
AFC output enabled
400µA gives 1.5V deadband window
1KΩ load, See note 3 and 4
75KΩ load, See note 3 and 4
75KΩ load, See note 3 and 4
See notes 1, 3 and 4
1KΩ load, See note 2 and 4
1KΩ load, See note 3 and 4
1KΩ load, See note 3 and 4
Maximum load voltage drop 2V
55
75
450
0
25
32
25
2.0
20
0.5
0.25
570
25
38
240
1.2
95
700
39
300
-40
Value
Typ.
36
Max.
40
800
mA
MHz
dBm
dBm
MHz/V
%
MHz/V
KHz/°C
V/rad
V/rad
Ω
Ω
dB
MHz
Vp-p
Ω
Refer to application in Fig. 3
Refer to application in Fig. 3; with
13.5MHz p-p deviation
See note 5
See note 5
Differential loop filter
Single ended loop filter
Single ended
Single ended
Single ended
Single ended
Single ended
Preamp limiting
Units
Conditions
Note 1. Product of input modulation f
1
at 4.43MHz, 13.5MHz p–p deviation and f
2
at 6MHz p–p deviation, (PAL chroma and sound
subcarriers).
Note 2. Ratio of output video signal with input modulation at 1MHz, 13.5MHz p–p deviation, to output rms noise in 6MHz bandwidth
with no input modulation.
Note 3. Input test signal pre–emphasised video 13.5MHz p–p deviation. Output voltage 600mV pk–pk.
Note 4. See page 3
Note 5. Assuming operating frequency of 479.5MHz set with V
CC
@ 5.0V and ambient temperature of +20°C. Only applies to Application
shown in Fig. 3. also refer to Fig. 8.
2
Advance Information
TEST CONFIGURATION
SL1461SA
BASE BAND VIDEO 1V p–p
TV SAT TEST TX
ROHDE & SCHWARZ SFZ
VIDEO GENERATOR
ROHDE & SCHWARZ SGPF
RF CARRIER FREQ 479.5MHz
FM MODULATION 13.5MHz P–P
PRE–EMPHASISED VIDEO
MONTFORD
TEST OVEN
SL1461 TEST APPLICATION BOARD
See Fig. 3 for details
PRE EMPHASISED BASE BAND VIDEO
VIDEO AMPLIFIER/
DE EMPHASISED NETWORK
DE EMPHASISED BASE BAND VIDEO 1V p–p
VIDEO ANALYSER
ROHDE & SCHWARZ UAF
The video drive characteristics measurements were made using the above test configuration. The maximum figures recorded in
the Electrical Characteristics Table coincide with high temperatures and extremes of supply voltage. No adjustment to the recorded
figures has been made to compensate for the effects of temperature on the external components of the application test board, in
particular the varactor diodes. If operation of the device at high ambient temperatures is envisaged then attention to temperature
compensation of the external circuitry will result in performance figures closer to the stated typical figures.
Fig.2 SL1461SA block diagram
ABSOLUTE MAXIMUM RATINGS
All voltages are referred to V
EE
at 0V
Characteristics
Supply voltage
RF input voltage
RF input DC offset
Oscillator
±
DC offset
Video
±
DC offset
Video feedback
±
DC offset
Video output DC offset
AFC pump DC offset
AFC disable DC offset
AFC deadband DC offset
AGC bias DC offset
AGC output DC offset
Storage temperature
Junction temperature
MP16 package thermal resistance,
chip to ambient
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-55
Min.
-0.3
Typ.
7
2.5
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
V
CC
+0.3
125
150
111
Max.
V
Vp-p
V
V
V
V
V
V
V
V
V
V
°C
°C
°C/W
Conditions
3
SP1461SA
Advance Information
ABSOLUTE MAXIMUM RATINGS
cont.
All voltages are referred to V
EE
at 0V
Characteristics
MP16 package thermal resistance,
chip to case
Power consumption at 5.5V
ESD protection - pins 1 to 15
ESD protection - Pin 16
2
1.7
Min.
Typ.
41
250
Max.
°C/W
mW
kV
kV
Mil-std-883 method 3015 class 1
Mil-std-883 method 3015 class 1
Conditions
2K
AGC BIAS
RV1
50K
AFC WINDOW ADJUST
RV2
C1
47nF
C2
100nF
R1
1
2
16
15
100nF
27K
R6
C3
47 F
C4
+5V
1nF
C12
D1
BB515
C5
4K7
TP4
R5
1K2
R4
100pF
C11
C10
TP2
VIDEO OUTPUT
TP1
3
4
SL1461SA
14
13
12
11
10
9
BB515 470nF
D2
TP3
4n7
C6
R2
5K1
4K7
R3
C7
1nF
5
6
7
8
100pF
1K2
C9
47 F
C8
1nF
RF INPUT
Fig.3 Standard application circuit
FUNCTIONAL DESCRIPTION
The SL1461SA is a wideband PLL FM demodulator,
optimised for application in satellite receiver systems and
requiring a minimum external component count. It contains all
the elements required for construction of a phase locked loop
circuit, with the exception of tuning components for the local
oscillator, and an AFC detector circuit for generation of error
signal to correct for any frequency drift in the outdoor unit local
oscillator. A block diagram is contained in Fig. 2 and the
typical application in Fig. 3.
The internal pin connections are contained in Fig.6/6a
In normal applications the second satellite IF frequency
of typically 402 or 479.5MHz is fed to the RF preamplifier,
which has a working sensitivity of typically -40 dBm,
depending on application and layout. The preamplifier
contains an RF level detect circuit, which generates an AGC
signal that can be used for controlling the gain of the IF
amplifier stages, so maintaining a fixed level to the RF input
of the SL1461SA, for optimum threshold performance. The
bias point of the AGC circuit can be adjusted to cater for
variation in AGC line voltage requirement and device input
power. The typical AGC curves are shown in Fig. 9. It is
recommended that the device is operated with an input signal
between -30 and -35dBm. This ensures optimum linearity and
threshold performance, and gives a good safety margin over
the typical sensitivity of
-40dBm.
The output of the preamplifier is fed to the mixer section
which is of balanced design for low radiation. In this stage the
RF signal is mixed with the local oscillator frequency, which
is generatedby an on–board oscillator. The oscillator block
uses an external varactor tuned sustaining network and is
optimised for high linearity over the normal deviation range.
A typical frequency versus voltage characteristic for the
oscillator is contained in Fig. 7. The loop output is designed
to compensate for first order temperature variation effects;
the typical stability is shown in Fig. 8
The output of the mixer is then fed to the loop amplifier
around which feedback is applied to determine loop transfer
characteristic . Feedback can be applied either in differential
or single ended mode; if the appropriate phase detector gains
are assumed in calculating loop filters, both modes should
give the same loop response.
The loop amplifier drives a 75Ω output impedance buffer
amplifier, which can either be connected to a 75Ω load or used
to drive a high input impedance stage giving greater linearity
and approximately 6dB higher demodulated signal output
level.
4
Advance Information
DESIGN OF PLL LOOP PARAMETERS
R2
C1
SL1461SA
GAIN = K
D
VOLT/RAD
RF INPUT
R1
BASEBAND OUTPUT
GAIN = K
0
RAD SEC/VOLT
VCO
Fig.4
The SL1461SA is normally used as a type 1 second order
loop and can be represented by the above diagram. For such
a system the following parameters apply;
where:
K
0
is the VCO gain in radian seconds per volt
K
D
is the phase detector gain in volts per radian
n
is the natural loop bandwidth
is the loop damping factor
R1 is loop amplifier input impedance
Note:
K
0
is dependant on sensitivity of VCO used.
K
D
= 0.25V/rad single ended, 0.5V/rad differential
1
2
and
K
0
K
D
1
2
n
From these factors the loop 3dB bandwidth can be determined
from the following expression;
2
2
n
AFC FACILITY
The SL1461SA contains an analog frequency error
detect circuit, which generates DC voltage proportional to the
integral of frequency error. If the incident RF is high then the
AFC voltage increases, if low then the voltage decreases. The
AFC voltage can then be converted by an ADC to be read by
the micro controller for frequency fine tuning; if used in an I
2
C
system it is recommended the device is used with either the
SP5055 or SP5056 frequency synthesiser which contains an
internal ADC readable via the I
2
C bus.
The voltage corresponding to frequency alignment is
arbitrary and user defined; if used with the SP5055 it is
suggested the aligned voltage is 0.375 V
CC
, corresponding to
the centre code of the ADC on port 6.
The AFC detect circuit contains a deadband centre
around the aligned frequency. The deadband can be adjusted
from zero window to approximately 25MHz width assuming an
oscillator dF/dV of 15MHz/V. If the incident RF is within this
window the AFC voltage does not integrate, except by
component leakage.
With reference to Fig.5; in normal operation the
demodulated video is fed to a dual comparator where it is
compared with two reference voltages, corresponding to the
extremes of the deadband, or window. These voltages are
variable and set by the window adjust input.
The comparators produce two digital outputs
corresponding to voltages above or below the voltage
window, or frequency above or below deadband. These digital
control signals are used to control a complimentary current
source pump. The current signals are then fed to the input of
an amplifier which is arranged as an integrator, so integrating
the
pulses into a DC voltage.
If the frequency is correctly aligned both the current
source and sink are disabled, therefore the DC output voltage
remains constant. There will be a small drift due to component
leakage; the maximum drift can be calculated from;
5
Embedded System
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