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9397 750 13928 © Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Product data Rev. 03 – 23 August 2004 22 of 31
Philips Semiconductors
PNX2000
Audio video input processor
10.3 Audio DAC characteristics
[1] Allowed audio sample frequencies are 32 kHz, 44.1 kHz and 48 kHz. Default f
S
in I
2
S-bus master mode is 48 kHz.
The audio DACs are based on a switched-resistor architecture which acts as a controlled
voltage divider between the positive and negative references ADACn_P and ADACn_N.
Therefore all noise on the reference pins will spread directly to the associated output pin
ADACn. Consequently it is important to provide adequate filtering of the reference voltage
to allow optimum signal-to-noise performance. Also, the voltage difference between
ADACn_P and SDAC_3V3 should be kept to a minimum as any difference will degrade
distortion performance.
The DACs have an internal resolution of 4 bits, running at a clock frequency of 128 f
S
,
using a noise shaper circuit to shift the quantization noise to out-of-band frequencies. To
prevent HF overloading of the circuit that is driven by the DAC outputs, a 3.3 nF capacitor
should be used to filter off the HF signal content. Together with the DAC’s nominal output
impedance of 1 kΩ, a first order roll-off at approximately 50 kHz will result. One capacitor
is required for each DAC output, connected between ADACn and the corresponding
ADACn_N.
10.4 Timing
10.4.1 Clock
Crystal specification
The crystal oscillator can be used with an external crystal, or in bypass mode with external
clock signal, see Figure 4
.
Table 24: Dynamic characteristics: Audio DAC
Tamb = 0 °C to +70 °C for commercial unless otherwise specified.
Symbol Parameter Conditions Min Typ Max Unit
Audio DAC Outputs: ADAC1-12
f
s
audio sample frequency - 32 48
[1]
48 kHz
S/N Signal to Noise Ratio, CCIR-2 k
weighted
outputs muted; reference f = 2 kHz,
0 dBFS
-94 - dB
(THD+N)/S Total Harmonic Distortion + Noise to
Signal ratio
f =1 kHz; 0 dBFS; 22 kHz
measurement bandwidth
- −77 - dB
f
res
frequency response +/-1 dB <10 - 22.5 kHz
α
ct
crosstalk between adjacent DACs f = 1 kHz; 0 dBFS - −90 - dB