4
RECEPTION
Tuner / IF
Standard pin 11 pin 13 pin 14 pin 7pin 6pin 5
The tuner is known as a Ofront end� type tuner. This is
because the tuner block and IF block are both combined
B/GHLLLHH
into one complex module pack. Channel tuning is based
I, K1HLHHHH
on a frequency synthesis system with a frequency range
D/KHHLHHH
of 48.25 MHz up to 855.25 MHz including cable and
LHHHLLL
hyperband channels.
L?HHHHHL
In multistandard sets, both blocks are IIC-bus controlled.
The IIC-bus of the IF block has only one-way data traffic.
Pin 11 drives input switches of IC501. Pin 11 is normally
In BG standard sets, the IF block has no IIC-bus interface.
high. During channel search (APSi), pin 11 goes
low. A low level on pins 27 and 28 of IC501
Multistandard IF block
switches the video IF signal (instead of sound IF)
The filter SAW501 operates as a picture signal filter. The
to the FPLL block. This is because the video band
video IF signal is input to pins 28 and 29 of the Picture /
is wider, and thus channel finding is more reli-
Sound Detector circuit, IC501.
able.
The filters SAW502 (BG, DK, I, Nicam L) and SAW503
(Nicam LO, L/LO AM) operate as sound signal filters. Stand-
Pin 13 drives the group delay correction circuitry
ard selection takes place by diodes D501 and D502 and
transistors T502 and T503. Transistors are driven via pin 7
Pin 14 selects the output of the group delay correction
of the IIC-bus expander (IC502). Sound IF signals are input
circuitry
to pins 31/32 (BG, DK, I, Nicam L), 1/2 (Nicam LO) and 4/5
(AM L/LO) of the detector circuit.
Pin 7selects the correct sound IF filter
The AGC adjustment is implemented by potentiometer
Pin 6/5 drives input switches and AM demodulator, se-
P501 on pin 26. Pins 20 and 21 are inputs for standard
lects right modulation and VCO frequency
switches, which are controlled by the IIC-bus expander. The
AFC information is output from pin 11 to the tuner block
BG standard IF block
and onward to the IIC-bus. The AGC control is taken from
The BG IF block is considerably simpler than the
pin 27 to the tuner block. The tank coil of the FPLL-VCO is
multistandard IF block. Only one SAW filter is used and
connected between pins 14 and 19. This PLL reference coil
the IIC-bus expander, group delay correction circuitry as
determines the stopping place of the found channel dur-
well as several switching transistors are omitted.
ing the APSi. The VCO frequency is two times video carrier
During channel search (APSi), the microcontroller (pin 47)
frequency, 2 x 38.9 MHz = 77.8 MHz. For LO standard re-
drives transistor T501 to conduct. A low level on pins 27
quirements, the VCO frequency is switched to 67.8 MHz (2
and 28 switches the video IF signal to the FPLL block in
x 33.9 MHz) using standard switches on pins 20 and 21,
order to make channel finding more reliable.
and adjusted by the potentiometer P502 on pin 20.
Tuning
The sound IF signal is output from pin 8 and the AM signal
Tuning is based on the APSi system (Automatic Program
from pin 7 onwards to the Multistandard Sound Proces-
search, Sorting and channel identification). The naming and
sor, ICa2.
identification of the channels takes place using either the
The CVBS signal is output from pin 23 to the group delay
PDC (Program Delivery Code), VPS (Video Programming
correction circuitry and amplifiers consisting of transistors
System), NI (Nation Identification) or Teletext header. Chan-
T504...514 and associated components. The CVBS signal
nel sorting is country dependant, and is therefore deter-
is then fed to the Video Matrix Switch, ICq1.
mined beforehand by the software.
The circuit IC502 operates as an IIC-bus expander (8-bit
shift register). Transistors T515 and T516 disconnect the
IIC-bus from pins 2 and 3 in order to eliminate possible
malfunctions on the IIC-bus when the TV set is switched
off. Standard definition takes place via the IIC-bus. The
microcontroller sends data to the shift register, the out-
puts change their state according to the data and strobe
pulse latches the outputs. The strobe pulse (high level) is
taken from the microcontroller (pin 47) to the base of tran-
sistor T517 and onward to pin 1. In addition, the base re-
sistor (R556) of T517 operates as an indication of the in-
stalled IF module version. The value of this resistor de-
pends on the module version. Pin 55 of the microcontroller
senses the voltage across this resistor and the base-emit-
ter junction , and thus identifies the module version.
The data from the microcontroller determines the outputs
of IC502 according to the transmission standard as follows: |
ACEC
HITACHI
