fc for LpOrder=1 (Hz)
參數資料
型號： XE8805AMI028LF
廠商： Semtech
文件頁數： 32/156頁
文件大?。?/td> 0K
描述： IC DAS 16BIT FLASH 8K MTP 64LQFP
標準包裝： 160
系列： XE880x
應用： 感測機
核心處理器： Coolrisc816?
程序存儲器類型： 閃存（22 kB）
控制器系列： XE8000
RAM 容量： 512 x 8
接口： UART，USRT
輸入/輸出數： 24
電源電壓： 2.4 V ~ 5.5 V
工作溫度： -40°C ~ 85°C
安裝類型： 表面貼裝
封裝/外殼： 64-LQFP
包裝： 托盤
供應商設備封裝： 64-LQFP（10x10）
產品目錄頁面： 585 (CN2011-ZH PDF)
配用： XE8000MP-ND - PROG BOARD AND PROSTART2 CARD
Semtech 2006
www.semtech.com
18-6
XE8805/05A
resolution (bit)
m
fc for LpOrder=1 (Hz)
fc for LpOrder=2 (Hz)
4
7812
31250
5
1953
11048
6
488
3906
7
122
1381
8
30
488
9
7.6
172
10
1.9
61
11
0.48
22
Table 18-5. Signal bandwidth as a function of the required resolution for the PWM without noise shaper (Fin=0,
NsOrder=00, fRC=2MHz).
18.4.3.2
Noise shaper of order 1 or 2
The calculation on the required low pass cut-off frequency given in 18.4.3.1 remains valid in this case. However,
the noise shaper allows using smaller PWM modulation for the same resolution. This increases the PWM
modulation frequency and as a consequence increases the output bandwidth.
An additional criterion however shows up: the filtering of the quantization noise. As can be seen from the examples
in 18.4.1, the interpolation between PWM codes generated by the noise shaper introduce sequences at
frequencies below the PWM modulation frequency. Assuming a low pass filter that has at least the same order as
the noise shaper, the resolution is given by (NsOrder
≥1) :
+
=
65
.
2
)
(
log
359
.
0
2
c
PWM
quant
f
NsOrder
m
resolution
The total resolution of the D/A is then the minimal of both criteria:
)
,
min(
PWM
quant
resolution
=
Table 18-6 and Table 18-7 show the signal bandwidth that can be obtained as a function of required resolution and
PWM modulation for first and second order noise shapers. It can be seen that these options are useful to obtain
high resolution using low PWM modulation m. For high PWM modulation m, the resolution is limited by the PWM
modulator and adding a noise shaper does not change anything.
NsOrder=1, fRC=2MHz, Fin=0, LpOrder=2
Resolution
PWM modulation m
(bit)
456
789
10
11
8
1596.4
976.6
488.3
244.1
122.1
61.0
9
798.2
690.5
345.3
172.6
86.3
43.2
10
399.1
244.1
122.1
61.0
30.5
11
199.5
172.6
86.3
43.2
21.6
12
99.8
61.0
30.5
15.3
13
49.9
43.2
21.6
10.8
14
24.9
15.3
7.6
15
12.5
10.8
5.4
16
6.2
3.8
Table 18-6. Low pass cut-off frequency as a function of the selected PMW modulation and required resolution for a
first order noise shaper.
Not
Recommended
for
New
Designs
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