Adc Transfer Function; Changes To Single-Ended Mode Section And Differential Section - Analog Devices ADuCM320 Hardware Reference Manual

ADuCM320 Hardware Reference Manual

ADC TRANSFER FUNCTION

Single-Ended Mode
In single-ended mode, the input range is 0 to V
1 LSB = FS/65,536; or,
V /65,536 = 2.51 V/65,536 = 38.30 μV
REF
The data values in ADCDATx are aligned such that the MSB is in ADCDATx[27] and, therefore, the LSB is in ADCDATx[12]. The ideal
code transitions occur midway between successive integer LSB values (that is, 1/2 LSB, 3/2 LSB, 5/2 LSB, ..., FS − 3/2 LSB). The ideal
input/output transfer characteristic is shown in Figure 6.
Differential Mode
The amplitude of the differential signal is the difference between the signals applied to the AIN+ and AIN− pins (that is, AIN+ − AIN−).
The maximum amplitude of the differential signal is, therefore, −V
(CM). The common mode is the average of the two signals (AIN+ + AIN−)/2 and is, therefore, the voltage that the two inputs are
centered on. This results in the span of each input being CM ± V
V . The voltage at the AIN+ and AIN− pins must be within the allowed input voltage range.
REF
The output coding is twos complement in fully differential mode, with
1 LSB = 2 × V /65,536; or,
REF
2 × 2.51 V/65,536 = 76.60 μV
where V = 2.51 V.
REF
The data values in ADCDATx are aligned such that the MSB is in ADCDATx[27] and, therefore, the LSB is in ADCDATx[13]. The ideal
input/output transfer characteristic is shown in Figure 7.
. The output coding is straight binary with
REF
ADCDATx[31:12]
0000 1111 1111 1111 1111
0000 1111 1111 1111 1110
0000 1111 1111 1111 1101
0000 1111 1111 1111 1100
1LSB =
0000 0000 0000 0000 0011
0000 0000 0000 0000 0010
0000 0000 0000 0000 0001
0000 0000 0000 0000 0000
0V 1LSB
NOTES
1. IN ADCDATx, x IS 0 TO 27, AS SHOWN IN TABLE 10.
Figure 6. ADC Transfer Function: Single-Ended Mode
REF
ADCDATx[31:12]
0000 0000 1111 1111 1110
1LSB =
0000 0000 1111 1111 1100
0000 0000 1111 1111 1010
0000 0000 0000 0000 0010
0000 0000 0000 0000 0000
1111 1111 1111 1111 1110
1111 0000 0000 0000 0100
1111 0000 0000 0000 0010
1111 0000 0000 0000 0000
–V + 1LSB
REF
NOTES
1. IN ADCDATx, x IS 0 TO 27, AS SHOWN IN TABLE 10.
Figure 7. ADC Transfer Function: Differential Mode
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V
REF
65536
V – 1LSB
REF
VOLTAGE INPUT
to +V p-p (2 × V ). This is regardless of the common mode
REF REF REF
/2. This voltage must be set up externally, and its range varies with
2 × V
REF
65536
0LSB +V – 1LSB
REF
VOLTAGE INPUT (V + – V –)
IN IN
UG-498