CXA3050M
NICAM and SMATV RF MODULATOR/PLL
Description
Fully synthesized I
2
C controlled UHF/VHF TV RF
Modulator compatible with PAL and NTSC video
formats.
Features
•
Minimal adjustment of external components
•
For use on VHF and UHF TV Frequencies
•
Video RF carrier frequency programmable in 125kHz
steps
•
Accepts NICAM 6.552MHz QPSK input signal
•
Accepts FM Stereo input signal
•
I
2
C control of:
a. Video RF Carrier Frequency
b. Sound Carrier Frequency
c. Modulation Depth (±2% Typ.)
d. FM Deviation (±8% Typ.)
e. P/S ratio (±1dB Typ.)
f. Nicam output enable to sleep
g. Video RF carrier enable to sleep
•
On chip Regulator 3.1V
Block Diagram
Analog GND
Analog V
CC
NICAM-in
OSC V
CC
24 pin SOP (Plastic)
Structure
Bipolar silicon monolithic IC
Applications
•
PAL and NTSC System VCR
•
Satellite Receiver
•
Set Top Box
•
SMATV
Recommended Operating Voltages
(Ta = 25°C)
•
Supply voltage
V
CC
5.0 ± 0.5
V
•
Supply for VCO Varactor
30 ± 0.5
V
•
Operating Temperature
–10 to +80 °C
RF-OUT
OSC GND
OSC4
OSC1
OSC2
PDout
14
PLL
PLL
11
OSC3
24
23
22
21
20
19
18
17
16
15
13
AMP
NICAM
MIXER
VIDEO
MIXER
AMP
VCO
AMP
TPSG
W/C-CLAMP
FM-OSC
REG
PLL
OSC
I
2
C-Interface
1
2
3
4
5
6
7
8
9
10
12
Vreg
Digital-V
CC
Mod-adj
Digital GND
Audio-Loop
filter
Video-in
Audio-in
SCL
Sony reserves the right to change products and specifications without prior notice. This information does not convey any license by
any implication or otherwise under any patents or other right. Application circuits shown, if any, are typical examples illustrating the
operation of the devices. Sony cannot assume responsibility for any problems arising out of the use of these circuits.
FM-Tank
–1–
SDA
Xtal
NC
EF
E96331A66-ST
CXA3050M
Functional Description of RF Modulator System
A block diagram of the RF modulator is shown in Fig. 1.
The composite video signal passes through an amplitude limiting circuit and a digitally controlled modulation
depth adjustment circuit. By means of three allocated I
2
C control bits it is possible to adjust the modulation
depth from a nominal 74% to 86% in 2.0% steps. Modulation depth can also be controlled externally by
addition of an external resistor on pin3. The video signal is then passed through to the mixer. In the mixer
stage, both the video composite signal and FM sound carrier amplitude modulate the RF carrier from the UHF
OSC, and the issuing signal is fed to the output via an RF amplifier.
The audio signals enter the chip via pin4. The FM Voltage Controlled Oscillator is band-switched to the
approximate centre frequencies of the four sound carrier frequencies 4.5MHz (NTSC) or 5.5, 6.0, 6.5MHz
(PAL). The required correct audio carrier frequency is fine tuned by the adjustment of fsound via I
2
C, where
upon the FM phase locked loop will lock the VCO onto the exact centre frequency. Minimum distortion of the
FM signal occurs when the centre frequency of the oscillator coincides with a mid-rail control voltage
(to 2.0V). Hence fine adjustment capacitors are also integrated on the chip, which tag into account any
capacitance variations from one batch to another. This is achieved by fine adjustment of Delta fsound via I
2
C
control. The design of the FM modulator eliminates the need for an external varactor.
The amplitude of the FM signal is varied via I
2
C by a digitally controlled logarithmic gain stage, which controls
the picture to sound power ratio (P/S). This signal is then fed into the RF amp. Hence at the RF output the P/S
ratio can be programmed in 1dB steps between the range 10dB and 17dB (see Electrical Characteristics).
Audio sensitivity can be programmed in 8% steps between the range –32% and +24%.
The UHF is phase locked to the reference frequency by means of the UHF phase locked loop. The VCO
output passes through a prescaler (≈8) followed by an I
2
C controlled programmable divider (≈M), and then
phase compared with that of a reference signal at 15.625kHz. The reference signal is derived from a 4MHz
crystal oscillator feeding a –256 divider. The UHF oscillator covers the frequency range 471MHz to 855MHz in
frequency steps of 125kHz. This is adequate for the UHF NTSC and PAL TV channels (471.25MHz (CH21) to
855.25MHz (CH69)). By adjustment of the external components around the oscillator and some adjustment to
output matching the RF modulator can also achieve range of frequencies in the VHF range.
The Nicam input (pin 22) accepts the 6.522MHz Nicam signal subcarrier QPSK at 728K bits/s data. This is
then buffered and feed into a separate mixer (controlled via VCO). This then feeds to the RF amp with the
composite video and audio. The I
2
C control will switch the Nicam signal output off or on.
–3–
CXA3050M
Software Application Notes
The minimum requirement to drive the CXA3050 and I
2
C bus drive is a 386/486 with 4M bytes hard disk
space, 16MHz clock speed and running DOS5.00 or above. Insert the disc into the drive and type TESTS and
at the prompt type iic. At this there should appear a single list of user friendly functional tests that can be
changed by keyboard manipulation. As an aid the test list is written below. Note Page up increments the
status, page down decrements the status.
Function
RF Output Power
Delta Sound
Nominal Status
1/0
1
Comments
Turns RF Amp, OSC on/off
Fine tune audio carrier
Course adjust for
4.5MHz (0)
5.5MHz (1)
6.0MHz (2)
6.5MHz (3)
Check listing on page 10 for
frequency to hex conversation
Ranges mod depth from
72% to 86%, 80% (4)
Sensitivity adjustable
Programmable in 8 steps of 1dB
Nicam Mixer on
Increase Video modulation ratio
Fsound
0
Frequency mode
Mod depth
FM Deviation
P/S Ratio
Nicam on/off
Over Mod on/off
2 to 8191
4
4
4
1/0
1/0
–5–
ADI Reference Circuit
京公网安备 11010802033920号
EEWORLD
