MSP 3400C
PRELIMINARY DATA SHEET
DCO1
ADR_DA
Oscillator
FIR_REG_1
Lowpass
MODE_REG[8]
Phase
Differen-
tiator
Phase and
AM Dis-
Mixer
crimination
FM2
Mute
Lowpass
Mixer
VREFTOP
MSPC sound IF channel 1
(MSP-CH1: FM2)
Amplitude
Carrier
Detect
AD_CV[7:1]
IDENT
ANA_IN1+
ANA_IN2+
AGC
AD
AD_CV[9,10,11]
Carrier
Detect
AD_CV[8]
MSPC sound IF channel 2
(MSP-CH2: FM1, AM)
Amplitude
ANA_IN–
Phase and
AM Dis-
crimination
FM1/AM
Mute
Lowpass
Mixer
Lowpass
Differen-
tiator
Phase
FIR_REG_2
FRAME
MODE_REG[8]
Pins
Oscillator
DCO2
FM2
Internal signal lines
Control registers
DCO2
Fig. 4–2: Demodulator architecture
4.1.3. Lowpass Filtering Block for Mixed Sound IF
Signals
cy of 32 kHz. The usable bandwidth of the final base-
band signals is about 15 kHz.
FM bandwidth limitation is performed by a linear phase
Finite Impulse Response (FIR-filter). Just like the oscil-
lators’ increments, the filter coefficients are program-
mable and are written into the IC by the CCU via the con-
trol bus. Two not necessarily different sets of coefficients
are required, one for channel 1 (FM2) and one for chan-
nel 2 (FM1=FM-mono). In section 6.2.4., several coeffi-
cient sets are proposed.
4.1.7. High Deviation FM Mode
By means of MODE_REG [9], the maximum FM-devi-
ation can be extended to approximately $360 kHz.
SincethismodecanbeappliedonlyfortheMSPCsound
IF channel 2, the corresponding matrices in the base-
band processing must be set to sound A. Apart from this,
the coefficient sets 380 kHz FIR_REG2 or 500 kHz
FIR_REG2 must be chosen for the FIR_REG_2. For a
given deviation, in relation to the normal FM-mode, the
audio level of the high-deviation mode is reduced by
6 dB.
4.1.4. Phase and AM Discrimination
The filtered sound IF signals are demodulated by means
of the phase and amplitude discriminator block. On the
output, the phase and amplitude is available for further
processing. AM signals are derived from the amplitude
information, whereas the phase information serves for
FM demodulation.
4.1.8. MSPC-Mute Function in the Dual Carrier FM
Mode
To prevent noise effects or FM identification problems in
the absence of one of the two FM carriers, the
MSP 3400 C offers a carrier detection feature, which
must be activated by means of AD_CV[9]. The mute lev-
el may be programmed by means of AD_CV[10,11].
(see section 6.2.1.) If no FM carrier is available at the
MSPC channel 1, the corresponding channel FM2 is
muted. If no FM carrier is available at the MSPC channel
2, the corresponding channel FM1 is muted. In case of
the absence of both FM carriers, pure noise will be am-
plified by the input AGC. Therefore, a proper mute func-
tion depends on the noise quality of the TV set’s IF part
and cannot be guaranteed. The mute function is not rec-
ommended for the satellite mode.
4.1.5. Differentiators
FM demodulation is completed by differentiating the
phase information output.
4.1.6. Lowpass Filter Block for Demodulated
Signals
The demodulated FM and AM signals are further low-
pass filtered and decimated to a final sampling frequen-
10
MICRONAS INTERMETALL
MICRONAS [ MICRONAS ]
