tda1548tz NXP Semiconductors, tda1548tz Datasheet - Page 7

• Manufacturer Part Number: tda1548tz
• Description: Bitstream Continuous Calibration Filter-dac With Headphone Driver And Dsp
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Soft mute
Soft mute is controlled by MUTE (pin 16). When the input
is active HIGH the value of the sample is decreased
smoothly to zero following a raised cosine curve.
32 coefficients are used to step down the value of the data,
each one being used 32 times before stepping on to the
next. This amounts to a mute transition time of 23 ms at
f
samples are returned to the full level again following a
raised cosine curve with the same coefficients being used
in the reverse order. Mute is synchronized to the sample
clock, so that the operation always takes place on
complete samples.
Digital sound processing features
B
A strong bass boost effect, which is useful in
compensating for poor bass response of portable
headphone sets, is implemented digitally in the TDA1548T
and can be controlled by ADBB (pin 20) and AD3S
(pin 22). Table 3 shows the bass boost values at different
input voltages. Table 4 shows the selection mode status
(flat/min/max) at different input voltages. Valid settings
range from “flat” (no influence on audio) to +18 dB with
step sizes of 2 dB in “minimum” and to +24 dB with step
sizes of 2 dB in “maximum”. The programmable bass
boost filter is a second-order shelving type with a fixed
corner frequency of 130 Hz for the “minimum” setting and
a fixed corner frequency of 230 Hz for the “maximum”
setting and has a Butterworth characteristic. Because of
the exceptional amount of programmable gain, bass boost
should be used in conjunction with adequate prior
attenuation, using the volume control.
T
A treble effect is implemented digitally in the TDA1548T
and can be controlled by ADTR (pin 19) and AD3S
(pin 22). Table 3 shows the treble values at different input
voltages. Table 4 shows the selection mode status
(flat/min/max) at different input voltages. Valid settings
range from “flat” (no influence on audio) to +6 dB with step
sizes of 2 dB in “minimum” and to +6 dB with a step size of
2 dB in “maximum”. The programmable treble filter is a
first-order shelving type with a fixed corner frequency of
2.8 kHz for the “minimum” setting and a fixed corner
frequency of 5.0 kHz for the “maximum” setting.
D
De-emphasis is controlled by DEEM (pin 15). The digital
de-emphasis filter is dimensioned to produce the
1995 Nov 15
s
REBLE
ASS BOOST
E
= 44.1 kHz. When MUTE is released (LOW), the
Bitstream continuous calibration filter-DAC
with headphone driver and DSP
-
EMPHASIS
7
de-emphasis frequency characteristics for the sample rate
44.1 kHz. With its 18-bit dynamic range, the digital
de-emphasis of the TDA1548T is a convenient and
component-saving alternative to analog de-emphasis.
When the DEEM pin is active HIGH, de-emphasis is
enabled. De-emphasis is synchronized to the sample
clock, so that operation always takes place on complete
samples.
Oversampling filter and noise shaper
The digital filter is a four times oversampling filter.
It consists of two sections which each increase the sample
rate by 2.
The second order noise shaper operates at 64f
in-band quantization noise to frequencies well above the
audio band. This noise shaping technique, used in
combination with a sign-magnitude coding, enables high
signal-to-noise ratios to be achieved. The noise shaper
outputs a 5-bit PDM bitstream signal to the DAC.
Continuous calibration DAC
The dual 5-bit DAC uses the continuous calibration
technique. This method, based on charge storage,
involves exact duplication of a single reference current
source. In the TDA1548T, 32 such current sources
plus 1 spare source are continuously calibrated.
The spare source is included to allow continuous converter
operation.
The DAC receives a 5-bit data bitstream from the noise
shaper. This data is converted to a sign-magnitude code
so that no current is switched to the output during digital
silence (input 00000H). In this way very high
signal-to-noise performance is achieved.
Component-saving stereo headphone driver
High precision, low-noise amplifiers together with the
internal conversion resistors R
the converter output current to a voltage capable of driving
a line output or headphone. The voltage is available at
VOL and VOR (0.64 V RMS typical).
A major component saving feature of the TDA1548T is that
no DC-blocking capacitors are needed in the application,
despite the asymmetrical supply. The V
is biased to the same voltage that the right and left channel
voltage outputs are, V
of left and right channel load currents. Therefore,
connecting a load between one of the outputs and V
only gives rise to a negligible amount of DC current
through the load.
ref
, and is capable of sinking the sum
CONV1
Product specification
and R
TDA1548T
COM
CONV2
output, pin 2,
s
. It shifts
convert
COM