参数资料
型号: AD7766BRUZ-RL7
厂商: Analog Devices Inc
文件页数: 8/25页
文件大小: 0K
描述: IC ADC 24BIT 128KSPS SAR 16TSSOP
标准包装: 1,000
位数: 24
采样率(每秒): 128k
数据接口: 串行
转换器数目: 1
功率耗散(最大): 18mW
电压电源: 模拟和数字
工作温度: -40°C ~ 105°C
安装类型: 表面贴装
封装/外壳: 16-TSSOP(0.173",4.40mm 宽)
供应商设备封装: 16-TSSOP
包装: 带卷 (TR)
输入数目和类型: 1 个差分,单极
配用: EVAL-AD7766EDZ-ND - BOARD EVAL AD7766 128KSPS 108DB
EVAL-AD7766-2EDZ-ND - BOARD EVAL AD7766-2 32KSPS 114DB
EVAL-AD7766-1EDZ-ND - BOARD EVAL AD7766-1 64KSPS 111DB
AD7766
Rev. C | Page 15 of 24
THEORY OF OPERATION
The AD7766/AD7766-1/AD7766-2 operate using a fully
differential analog input applied to a successive approximation
(SAR) core. The output of the oversampled SAR is filtered using
a linear-phase digital FIR filter. The fully filtered data is output
in a serial format, with the MSB being clocked out first.
AD7766/AD7766-1/AD7766-2 TRANSFER
FUNCTION
The conversion results of the AD7766/AD7766-1/AD7766-2
are output in a twos complement, 24-bit serial format. The fully
differential inputs VIN+ and VIN are scaled by the AD7766/
AD7766-1/AD7766-2 relative to the reference voltage input
(VREF+) as shown in Figure 28.
06
44
9-
01
2
100 ... 000
100 ... 001
111 ... 110
111 ... 111
000 ... 000
000 ... 001
000 ... 010
011 ... 110
011 ... 111
24
-B
IT
O
U
T
P
U
T
24 BITS
TWOS
COMPLEMENT
VIN+ = 0V
VIN+ = VREF+ – 1LSB
VIN– = VREF+ – 1LSB
VIN– = 0V
VIN+ =
VREF+
2
VIN– =
VREF+
2
Figure 28. AD7766/AD7766-1/AD7766-2 Transfer Function
CONVERTER OPERATION
Internally, the input waveform applied to the SAR core is
converted and an equivalent digital word is output to the digital
filter at a rate equal to MCLK. By employing oversampling, the
quantization noise of the converter is spread across a wide
bandwidth from 0 to fMCLK. This means that the noise energy
contained in the signal band of interest is reduced (see
QUANTIZATION NOISE
BAND OF INTEREST
fMCLK/2
06
44
9-
2
13
Figure 29. Quantization Noise
DIGITAL FILTER CUTOFF FREQUENCY
fMCLK/2
BAND OF INTEREST
0
64
49
-2
14
Figure 30. Digital Filter Cutoff Frequency
The digital filtering that follows the converter output acts to
remove the out-of-band quantization noise (see Figure 30). This
also has the effect of reducing the data rate from fMCLK at the
input of the filter to fMCLK/8, fMCLK/16, or fMCLK/32 at the digital
output, depending on which model of the device is being used.
The digital filter consists of three separate filter blocks. Figure 31
shows the three constituent blocks of the filter. The order of
decimation of the first filter block is set as 2, 4, or 8. The
remaining sections each operate with a decimation of 2.
06
44
9-
0
1
9
STAGE 1
STAGE 2
DIGITAL FILTER
STAGE 3
SINC FILTER
FIR FILTER
DEC × (2 × n)
DEC × 2
DATA
STREAM
SDO
Figure 31. FIR Filter Stages
(n = 1 for AD7766, n = 2 for AD7766-1, n = 4 for AD7766-2)
Table 6 shows the three available models of the AD7766, listing
the change in output data rate relative to the order of decimation
rate implemented. This brings into focus the trade-off that exists
between extra filtering and reduction in bandwidth, whereby
using a filter option with a larger decimation rate increases the
noise performance while decreasing the usable input bandwidth.
Table 6. AD7766 Models
Model
Decimation Rate
Output Data Rate (ODR)
AD7766
8
128 kHz
AD7766-1
16
64 kHz
AD7766-2
32
32 kHz
Note that the output data rates shown in Table 6 are realized
when using the maximum MCLK input frequency of 1.024 MHz.
The output data rate scales linearly with the MCLK frequency,
as does the digital power dissipated in the device.
The settling time of the filter implemented on the AD7766,
AD7766-1, and AD7766-2 is related to the length of the filter
employed. The response of the filter in the time domain sets the
filter settling time. Table 7 shows the filter settling times of the
AD7766/AD7766-1/AD7766-2.
The frequency responses of the digital filters on the AD7766,
AD7766-1, and AD7766-2 are shown in Figure 32, Figure 33,
and Figure 34, respectively. At the Nyquist frequency (output
data rate/2), the digital filter provides 6 dB of attenuation. In each
case, the filter provides stop-band attenuation of 100 dB and
pass-band ripple of ±0.005 dB.
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