SAA7712H Datasheet, PDF (18/44 Pages) NXP Semiconductors – Sound effects DSP

Philips Semiconductors
Sound effects DSP
Preliminary specification
SAA7712H
handbook, full pagewidth
A IN0
B IN1
C IN2
D IN3
1
2
3
4
5
2 channel
OUT0
2 channel
OUT1
OUT2
OUT3
MGS213
Fig.8 Configurations of the equalizer sections.
8.3.3 OVERFLOW DETECTION
The equalizer has an overflow flag. This flag is fed to
output pin EQOV. If an overflow is detected in one of the
filter sections, the signal is clipped to the maximum
allowed level. The overflow flag is immediately set.
It remains at a HIGH-level during the remaining part of the
current audio sample period and for the whole next sample
period. If no overflow is detected during this next sample
period, the overflow flag goes to a LOW-level at the
beginning of the sample period after that. Otherwise, the
overflow flag remains at a HIGH-level for at least one other
audio sample period.
8.4 Clock circuit and oscillator
8.4.1 GENERAL DESCRIPTION
The chip has a crystal clock oscillator. It can use a crystal
at either f_xtal = 16.384 MHz = 512 × 32 kHz or
f_xtal = 18.432 MHz = 576 × 32 kHz in fundamental mode.
The block diagram of this Pierce oscillator is shown in
Fig.9. The active element needed to compensate for the
loss resistance of the crystal is the block Gm. This block is
placed between the external pins OSC_IN
and OSC_OUT.
The gain of the oscillator is internally controlled by the
AGC block. A sine wave with a peak-to-peak voltage close
to the oscillator power supply voltage is generated.
The AGC block prevents clipping of the sine wave and
therefore the higher harmonics are as low as possible.
At the same time, the voltage of the sine wave is as high
as possible so reducing the jitter going from sine wave to
clock signal. The sinusoidal output is converted into a
CMOS compatible clock by the comparator.
The second mode of operation shown in Fig.10, is the
slave mode which is driven by a master clock directly.
The signal to pin OSC_IN can be driven to the power
supply voltages V_{DD_OSC} and V_{SS_OSC}.
8.4.2 SUPPLY OF THE CRYSTAL OSCILLATOR
The power supply connections of the oscillator are
separate from the other supply lines. This is to minimize
the feedback from the ground bounce of the chip to the
oscillator circuit. Pin V_{SS_OSC} is used as the ground supply
and pin V_{DD_OSC} as the positive supply.
1999 Aug 05
18