参数资料
型号: TSC2300IPAGRG4
厂商: TEXAS INSTRUMENTS INC
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PQFP64
封装: GREEN, PLASTIC, TQFP-64
文件页数: 60/83页
文件大小: 1268K
代理商: TSC2300IPAGRG4
www.ti.com
N0 ) 2 N1 Z–1 ) N2 Z–2
32768–2 D1 Z–1–D2 Z–2
N3 ) 2 N4 Z–1 ) N5 Z–2
32768–2 D4 Z–1–D5 Z–2
(12)
TSC2300
SLAS372 — NOVEMBER 2002
Conventional audio DAC designs utilize high-order analog filtering to remove quantization noise that falls within the
audio band when operating at low sample rates. Here, however, the increased oversampling at low sample rates keeps
the noise above 20 kHz, yielding a similar noise floor out to 20 kHz whether the sample rate is 8 kHz or 48 kHz. If the
audio bypass path is not in use when the stereo DAC is in use, the user should power down the bypass path, as this
improves DAC SNR and reduces power consumption.
In addition, the digital interpolation filter provides enhanced image filtering to reduce signal images caused by the
upsampling process that land below 20 kHz. For example, upsampling an 8-kHz signal produces signal images at
multiples of 8 kHz, i.e., 8 kHz, 16 kHz, 24 kHz, etc. The images at 8 kHz and 16 kHz are below 20 kHz and thus are
still audible to the listener, therefore they must be filtered heavily to maintain a good quality output. The interpolation
filter is designed to maintain at least 65-dB rejection of signal images landing between 0.55 Fs and 3.5 Fs, for all
sample rates, including any images that land within the audio band (20 Hz-20 kHz). Passband ripple for all sample-rate
cases (from 20 Hz to 0.4535 Fs) is +/-0.1-dB maximum.
The analog reconstruction filter design consists of a switched-capacitor filter with one pole and three zeros. The
single-bit data operates at 128 x 48 kHz = 6.144 MHz (for selected sample-rates that are submultiples of 48 kHz) or at
128 x 44.1 kHz = 5.6448 MHz (for selected sample-rates that are submultiples of 44.1 kHz). The interpolation filter
takes data at the selected sample-rate from the effects processing block, then performs upsampling and image filtering,
yielding a 6.144-MHz or 5.6448-MHz data stream, which is provided to the digital delta-sigma modulator.
Audio DAC SNR performance is 98-dB-A typical over 20 Hz - 20 kHz bandwidth in 44.1/48-kHz mode at the
line-outputs with a 3.3-V supply level.
DAC Digital De-emphasis
The DAC digital effects processing block can perform several operations on the audio data before it is passed to the
interpolation filter. One such operation is a digital de-emphasis, which can be enabled or disabled by the user via the
DEEMP bit (Bit 0, Reg 05h, Pg 2). This is only available for sample rates of 32 kHz, 44.1 kHz, and 48 kHz. The
transfer function consists of a pole with time constant of 50 sec and a zero with time constant of 15 sec.
DAC Programmable Digital Effects Filter
The DAC digital effects processing block also includes a fourth order digital IIR filter with programmable coefficients
(independently programmable per channel). The filter transfer function is given by:
The N and D coefficients are set via SPI registers, and this filter can be enabled or disabled via the BASS bit (Bit 1,
Reg 05h, Pg ú2). This functionality can implement a number of different functions, such as bass-boost (default),
treble-boost, mid-boost, or other equalization. This transfer function(s) can be determined by the user and loaded to
the TSC2300 at power-up, and the feature can then be switched on or off by the user during normal operation.
The default coefficients at reset are given by:
N0=N3=27618
D1=D4=32130
N1=N4=-27033
D2=D5=-31505
N2=N5=26461
which implements the bass-boost transfer function shown in Figure 77, having a 3-dB attenuation for signals above
approximately 150 Hz when operating at a 48-kHz sampling rate. All coefficients are represented by 16-bit twos
complement integers with values ranging from -32768 to +32767.
63
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