TDA8415 Datasheet, PDF (5/19 Pages) NXP Semiconductors – TV and VTR stereo/dual sound processor with integrated filters and I2C-bus control

Philips Semiconductors
TV and VTR stereo/dual sound processor
with integrated filters and I²C-bus control
Preliminary specification
TDA8415
PINNING
1
2
3
4
5
6
7
8
9
10
Control port C1
SDA, serial data line (I²C-bus)
SCL, serial clock line (I²C-bus)
Oscillator input (or quartz)
Digital ground (0 V)
Not connected, but reserved
Sound channel input AF2 (E2)
Sound channel input AF1 (E1)
External AF input (E4)
External AF input (E3)
11
Output A4 AF 2 output
12
Output A3 AF 2 output
13
Output A2 AF 1 output
13
Output A1 AF 1 output
15
Supply voltage V_P
16
Analogue ground (0 V)
17
Ripple rejection improvement
18
Mute input
19
Control port C2
20
Not connected, but reserved
FUNCTIONAL DESCRIPTION
Anti-aliasing filters
Frequency band limitation is performed by a second order Sallen and Key low-pass filter inserted in the AF signal path
and the identification circuit. This limitation is necessary because of the time-discrete signal processing needed to meet
the Nyquist criterion.
Identification
To enable the identification of the transmitted AF signal (mono, stereo or dual sound), the carrier frequency of the second
channel (E2) is also modulated by an identification signal. The identification signal is a 54.6875 kHz pilot carrier signal
which is 50% amplitude modulated by either a 117.4 Hz signal for stereo transmission or by a 274.1 Hz signal for dual
sound transmission.
The identification section of the circuit consists of a 54 kHz high-pass filter followed by a gain controlled amplifier with an
AM demodulator. The total gain of the high-pass filter and the amplifier is approximately 56 dB. The demodulated
identification signal is filtered by the identification band-pass filters, (117.4 Hz for stereo transmission, 274.1 Hz for dual
sound transmission). The output from either filter is converted to a DC signal by a peak detector and the necessary
hysteresis is performed by a Schmitt-trigger. The resultant DC output signals indicate the status of the transmitter (mono,
stereo or dual sound).
De-matrix and de-emphasis
Depending on the results of the identification circuit (mono, stereo or dual sound) the AF signals at the inputs E1 and E2
are converted to the signals at E1* and E2* as listed in Table 1.
Table 1 Transmitter status
TRANSMITTER STATUS ⁽¹⁾
mono
stereo
dual sound
E1
0.7(L+R)
0.7(L+R)
0.7A
E2
−
2R
B
E1*
2(L+R)
4L
2A
E2*
−
4R
2B
Note
1. Where L = left channel signal; R = right channel signal; A = first sound channel signal and B = second sound channel
signal.
This section of the circuit also performs the de-emphasis (50 µs time constant) with a high degree of accuracy.
May 1989
5