参数资料
| 型号： | AD7608BSTZ-RL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 19/32页 |
| 文件大小： | 0K |
| 描述： | IC DAS W/ADC 18BIT 8CH 64LQFP |
| 标准包装： | 1,500 |
| 类型： | 数据采集系统（DAS），ADC |
| 分辨率（位）： | 18 b |
| 采样率（每秒）： | 200k |
| 数据接口： | DSP，MICROWIRE?，并联，QSPI?，串行，SPI? |
| 电压电源： | 模拟和数字 |
| 电源电压： | 2.3 V ~ 5.25 V，4.75 V ~ 5.25 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 64-LQFP |
| 供应商设备封装： | 64-LQFP（10x10） |
| 包装： | 带卷 (TR) |
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AD7608
Data Sheet
Rev. A | Page 26 of 32
DIGITAL FILTER
The AD7608 contains an optional digital first-order sinc filter
that should be used in applications where slower throughput
rates are used or where higher signal-to-noise ratio or dynamic
range is desirable. The oversampling ratio of the digital filter is
controlled using the oversampling pins, OS [2:0] (see Table 8).
OS 2 is the MSB control bit, and OS 0 is the LSB control bit.
Table 8 provides the oversampling bit decoding to select the
different oversample rates. The OS pins are latched on the falling
edge of BUSY. This sets the oversampling rate for the next
conversion (see Figure 45). In addition to the oversampling
function, the output result is decimated to 18-bit resolution.
If the OS pins are set to select an OS ratio of 8, the next
CONVST x rising edge takes the first sample for each channel,
and the remaining seven samples for all channels are taken with
an internally generated sampling signal. These samples are then
averaged to yield an improvement in SNR performance. Table 8
shows typical SNR performance for both the ±10 V and the
±5 V range. As Table 8 indicates, there is an improvement in
SNR as the OS ratio increases. As the OS ratio increases, the
3 dB frequency is reduced, and the allowed sampling frequency
is also reduced. In an application where the required sampling
frequency is 10 kSPS, an OS ratio of up to 16 can be used. In
this case, the application sees an improvement in SNR, but the
input 3 dB bandwidth is limited to ~6 kHz.
The CONVST A and CONVST B pins must be tied/driven
together when oversampling is turned on. When the over-
sampling function is turned on, the BUSY high time for the
conversion process extends. The actual BUSY high time
depends on the oversampling rate selected: the higher
the oversampling rate, the longer the BUSY high, or total
conversion time (see Table 3).
Figure 44 shows that the conversion time extends as the over-
sampling rate is increased, and the BUSY signal lengthens for the
different oversampling rates. For example, a sampling frequency
of 10 kSPS yields a cycle time of 100 s. Figure 44 shows OS × 2
and OS × 4; for a 10 kSPS example, there is adequate cycle time to
further increase the oversampling rate and yield greater improve-
ments in SNR performance. In an application where the initial
sampling or throughput rate is at 200 kSPS, for example, and
oversampling is turned on, the throughput rate must be reduced
to accommodate the longer conversion time and to allow for the
read. To achieve the fastest throughput rate possible when over-
sampling is turned on, the read can be performed during the
BUSY high time. The falling edge of BUSY is used to update the
output data registers with the new conversion data; therefore, the
reading of conversion data should not occur on this edge.
CS
RD
DATA:
DB[15:0]
BUSY
CONVST A,
CONVST B
tCYCLE
tCONV
4s
t4
9s
19s
OS = 0 OS = 2 OS = 4
08938-
043
Figure 44. No Oversampling, Oversampling × 2, and Oversampling × 4 While
Using Read After Conversion
CONVST A,
CONVST B
BUSY
OS x
tOS_SETUP
tOS_HOLD
CONVERSION N
CONVERSION N + 1
OVERSAMPLE RATE
LATCHED FOR CONVERSION N + 1
08938-
042
Figure 45. OS Pin Timing
Table 8. Oversample Bit Decoding
OS [2:0]
OS Ratio
SNR ±5 V
Range (dB)1
SNR ±10 V
Range (dB)1
3 dB BW ±5 V
Range (kHz)
3 dB BW ±10 V
Range (kHz)
Maximum Throughput
CONVST x Frequency (kHz)
000
No OS
90.5
91.2
15
22
200
001
2
92.5
93.4
15
22
100
010
4
94.45
95.7
13.7
18.5
50
011
8
96.5
98
10.3
11.9
25
100
16
99.1
100.4
6
12.5
101
32
101.7
102.8
3
6.25
110
64
103
103.5
1.5
3.125
111
Invalid
1
SNR values taken with a full scale 100 Hz input signal.
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