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| 型号： | AD73322AR |
| 厂商： | ANALOG DEVICES INC |
| 元件分类： | 通信及网络 |
| 英文描述： | Low Cost, Low Power CMOS General-Purpose Dual Analog Front End |
| 中文描述： | SPECIALTY TELECOM CIRCUIT, PDSO28 |
| 封装： | SOIC-28 |
| 文件页数： | 26/40页 |
| 文件大小： | 437K |
| 代理商： | AD73322AR |
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REV. 0
AD73322L
–26–
As the AD73322L can be operated at 8 kHz (see Figure 22) or
16 kHz sampling rates, which make it particularly suited for voice-
band processing, it is important to understand the action of the
interpolator
’
s Sinc3 response. As was the case with the encoder
section, if the output signal
’
s frequency response is not bounded
by the Nyquist frequency, it may be necessary to perform some
initial digital filtering to eliminate signal energy above Nyquist
to ensure that it is not imaged at the integer multiples of the
sampling frequency. If the user chooses to bypass the interpo-
lator, perhaps to reduce group delay, images of the original
signal will be generated at integer intervals of the sampling fre-
quency. In this case these images must be removed by external
analog filtering.
FREQUENCY
–
Hz
0
500
0
–
10
d
–
20
–
30
–
40
–
50
–
60
1000
1500
2000
2500
3000
3500
4000
–
70
–
80
–
90
–
100
Figure 22. FFT (DAC 8 kHz Sampling)
Figure 23 shows the output spectrum of a 1 kHz tone being gener-
ated at an 8 kHz sampling rate with the interpolator bypassed.
FREQUENCY
–
Hz
0
0.5
0
d
–
20
1.0
1.5
2.0
2.5
3.0
3.5
–
100
–
10
–
30
–
40
–
50
–
60
–
70
–
80
–
90
10
4
Figure 23. FFT (DAC 8 kHz Sampling—Interpolator
Bypassed)
Decoder Group Delay
The interpolator roll-off is mainly due to its sinc-cubed function
characteristic, which has an inherent group delay given by the
equation:
Group Delay
(
Interpolator
) =
Order
×
(
L
–
1)/2)
×
T
INT
where:
Order
is the interpolator order (= 3),
L
is the interpolation factor (= 32 @ 64 kHz, = 64 @ 32 kHz,
= 128 @ 16 kHz, = 256 @ 8 kHz) and
T
INT
is the interpolation sample interval (= 1/2.048e6)
=> Group Delay (Interpolator @ 64 kHz)
= 3
×
(32
–
1)/2
×
(1/2.048e6)
= 22.7
μ
s
The analog section has a group delay of approximately 25
μ
s.
On-Chip Filtering
The primary function of the system filtering
’
s sinc-cubed (Sinc3)
response is to eliminate aliases or images of the ADCs or DAC
’
s
resampling, respectively. Both modulators are sampled at a nomi-
nal rate of DMCLK/8 (which is 2.048 MHz for a DMCLK of
16.384 MHz) and the simple, external RC antialias filter is
sufficient to provide the required stopband rejection above the
Nyquist frequency for this sample rate. In the case of the ADC
section, the decimating filter is required to both decrease sample
rate and increase sample resolution. The process of changing
sample rate (resampling) leads to aliases of the original sampled
waveform appearing at integer multiples of the new sample rate.
These aliases would get mapped into the required signal pass-
band without the application of some further antialias filtering.
In the AD73322L, the sinc-cubed response of the decimating
filter creates spectral nulls at integer multiples of the new sample
rate. These nulls coincide with the aliases of the original waveform
which were created by the down-sampling process, therefore
reducing or eliminating the aliasing due to sample rate reduction.
In the DAC section, increasing the sampling rate by interpola-
tion creates images of the original waveform at intervals of the
original sampling frequency. These images may be sufficiently
rejected by external circuitry but the sinc-cubed filter in the
interpolator again nulls the output spectrum at integer intervals
of the original sampling rate which corresponds with the images
due to the interpolation process.
The spectral response of a sinc-cubed filter shows the character-
istic nulls at integer intervals of the sampling frequency. Its
passband characteristic (up to Nyquist frequency) features a
roll-off that continues up to the sampling frequency, where the
first null occurs. In many applications this smooth response will
not give sufficient attenuation of frequencies outside the band of
interest; therefore, it may be necessary to implement a final filter
in the DSP which will equalize the passband roll-off and provide
a sharper transition band and greater stopband attenuation.
相关PDF资料 |
PDF描述 |
|---|---|
| AD73322AST | Low Cost, Low Power CMOS General-Purpose Dual Analog Front End |
| AD73322LAR | Low Cost, Low Power CMOS General-Purpose Dual Analog Front End |
| AD73322LAST | Low Cost, Low Power CMOS General-Purpose Dual Analog Front End |
| AD73322EB | Low Power 10MHz Current Feedback Amplifier; Package: SO; No of Pins: 8; Temperature Range: 0°C to +70°C |
| AD73322EZ | Precision Rail-to-Rail Input and Output Op Amp; Package: SO; No of Pins: 8; Temperature Range: 0°C to +70°C |
相关代理商/技术参数 |
参数描述 |
|---|---|
| AD73322AR-REEL | 制造商:Analog Devices 功能描述:Audio Codec 2ADC / 2DAC 16-Bit 28-Pin SOIC W T/R |
| AD73322AR-REEL7 | 制造商:Analog Devices 功能描述:Audio Codec 2ADC / 2DAC 16-Bit 28-Pin SOIC W T/R |
| AD73322ARZ | 制造商:Analog Devices 功能描述:Audio Codec 2ADC / 2DAC 16-Bit 28-Pin SOIC W 制造商:Analog Devices 功能描述:AUD CODEC 2ADC / 2DAC 16BIT 28SOIC - Trays 制造商:Analog Devices 功能描述:Dual Voice Band Codec 16-Bit 3/5V SOIC28 |
| AD73322ARZ-REEL | 制造商:Analog Devices 功能描述:DUAL VOICE BAND ANALOG FRONT END IC (ROHS) - Tape and Reel 制造商:Analog Devices 功能描述:DUAL VOICEBAND ANALOG FRONT END IC |
| AD73322ARZ-REEL7 | 制造商:Analog Devices 功能描述:DUAL VOICEBAND CODEC - Tape and Reel |
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