參數(shù)資料
型號: AD1953YSTZRL
廠商: Analog Devices Inc
文件頁數(shù): 8/36頁
文件大?。?/td> 0K
描述: IC DSP DAC AUDIO3CH/26BIT 48LQFP
產(chǎn)品培訓(xùn)模塊: Data Converter Fundamentals
DAC Architectures
標(biāo)準(zhǔn)包裝: 2,000
系列: SigmaDSP®
位數(shù): 26
數(shù)據(jù)接口: 串行
轉(zhuǎn)換器數(shù)目: 3
電壓電源: 模擬和數(shù)字
功率耗散(最大): 540mW
工作溫度: -40°C ~ 105°C
安裝類型: 表面貼裝
封裝/外殼: 48-LQFP
供應(yīng)商設(shè)備封裝: 48-LQFP(7x7)
包裝: 帶卷 (TR)
輸出數(shù)目和類型: 6 電壓,單極
采樣率(每秒): 48k
REV. 0
AD1953
–16–
INPUT WAVEFORM
HOLD TIME, SPI-
PROGRAMMABLE
RELEASE TIME, SPI-
PROGRAMMABLE
Figure 9. Using the Hold and Release Time Feature
Using this idea of a modified rms algorithm, the true rms value
is still obtained for all but the lowest frequency signals, while the
distortion due to rms ripple is reduced. It also allows the user to
set the hold and release times of the compressor independently.
The detector path of the AD1953 is shown in Figure 10. The rms
detector is controlled by three parameters stored in parameter
RAM: the rms time constant, the hold time, and the release rate.
The log output of the rms detector is applied to a look-up table
with interpolation. The higher bits of the rms output form an
offset into this table, and the lower bits are used to interpolate
between the table entries to form a high precision gain word.
The look-up table resides in the parameter RAM and is loaded
by the user to give the desired curve. The look-up table contains
33 data locations, and the LSB of the address into the look-up
table corresponds to a 3 dB change in the amplitude of the detec-
tor signal. This gives the user the ability to program an input/
output curve over a 99 dB range. For the main compressor, the
table resides in locations 110 to 142 in the SPI parameter RAM.
LOOK-UP TABLE
LINEAR
INTERPOLATION
MODIFIED RMS
DETECTOR WITH
LOG OUTPUT
OUTPUT TO
GAIN STAGE
HIGH BITS (1LSB = 3dB)
LOW BITS
TIME
CONSTANT
HOLD
RELEASE
Figure 10. Gain Derived from Interpolated Look-Up Table
One subtlety of the table look-up involves the difference between
the rms value of a sine wave and that of a square wave. If a
full-scale square wave is applied to the AD1953, the rms value of
this signal will be 3 dB higher than the rms value of a 0 dBFS sine
wave. Therefore, the table will range from +9 dB (location 142)
to –87 dB (location 110).
The entries in the table are linear gain words in 2.20 format.
Figure 11 shows an example of the table entries for a simple
above-threshold compressor.
INPUT LEVEL – 3dB/TABLE ENTRY
OUTPUT
LEVEL
dB
INPUT LEVEL – 3dB/TABLE ENTRY
LINEAR
GAIN
1.0
DESIRED
COMPRESSION
CURVE
Figure 11. Example of Table Entry for a Given
Compression Curve
Note that the maximum gain that can be entered in the table is 2.0
(minus 1 LSB). If more gain is required, the entire compression
curve may be shifted upward by using the post-compression gain
block following the compressor/limiter.
The AD1953 compressor/limiter also includes a look-ahead
compression feature. The idea behind look-ahead compression
is to prevent compressor overshoots by applying some digital
delay to the signal before the gain-control multiplier, but not to
the detector path. In this way, the detector can acquire the new
amplitude of the input signal before the signal actually reaches
the multiplier. A comparison of a tone burst fed to a conventional
compressor versus a look-ahead compressor is shown in Figure 12.
CONVENTIONAL COMPRESSOR GAIN
LOOK-AHEAD COMPRESSOR GAIN
HOLD TIME
Figure 12. Conventional Compression vs. Look-Ahead
Compression
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