adc12eu050eb National Semiconductor Corporation, adc12eu050eb Datasheet - Page 41

• Manufacturer Part Number: adc12eu050eb
• Description: Adc12eu050 Ultra-low Power, Octal, 12-bit, 40-50 Msps Sigma-delta Analog-to-digital Converter
• Manufacturer: National Semiconductor Corporation

Decimator Clipping Control Register
Address:
Attributes
Description
Default
Bit
5:3
2:0
7
6
CGS
b[7]
0
CGS: Custom Gain Setting. This bit is used to override the automatic gain settings for ADC and IOR
modes. If the user wishes to write a custom digital gain coefficient using a[2:0] and b[2:0] of this register,
then the CGS bit must be set.
Reserved. Write as zero for future compatibility.
a[2:0]: Digital Gain Coefficient. In clipping mode the input range of an ADC channel is limited to
1.56Vpp. In ADC mode the input range is 2.10Vpp. The output of the digital filter has to be scaled
according to the selected mode (the filter data has to be mapped in to the 12bit output data), the
difference between 1.6Vpp and 2.2Vpp is -2.6dB, hence the digital filter gain has to be set to 2.6dB
when in IOR mode and to 0dB when in clipping mode (default mode) . This is performed by setting a
Digital Gain Factor which is calculated using the following formula:
The mapping of the coefficient values for a[2:0] is as follows:
011 = Not used. Defaults to 2
010 = 2
001 = 1
000 = 0
111 = -1
110 = -2
101 = Not used. Defaults to -2
100 = Not used. Defaults to -2
The mapping of the coefficient values for b[2:0] is shown below. The table on the following page shows
the available Digital Gain Coefficient settings.
b[2:0]: Digital Gain Coefficient.
The mapping of the coefficient values for b[2:0] is as follows:
011 = Not used. Defaults to 2
010 = 2
001 = 1
000 = 0
111 = -1
110 = -2
101 = Not used. Defaults to -2
100 = Not used. Defaults to -2
0
1
Reserved
14h
Write Only.
Register 15h reads back contents of Register 14h.
b[6]
Normal operation Automatic gain settings used
Custom Gain Setting Gain setting from a[2:0] and b[2:0] used.
0
b[5]
0
a[2:0]
b[4]
0
41
Description
b[3]
0
b[2]
0
b[2:0]
b[1]
0
b[0]
0
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