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| 型號(hào)： | EVAL-ADUC7023QSPZ1 |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 28/96頁 |
| 文件大?。?/td> | 0K |
| 描述： | BOARD EVAL FOR ADUC7023 |
| 標(biāo)準(zhǔn)包裝： | 1 |
| 系列： | QuickStart™ PLUS 套件 |
| 類型： | MCU |
| 適用于相關(guān)產(chǎn)品： | ADuC7023 |
| 所含物品： | 板 |
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ADuC7023
Data Sheet
| Page 34 of 96
The C1 capacitors in Figure 27 are typically 4 pF and can be
primarily attributed to pin capacitance. The resistors are
lumped components made up of the on resistance of the
switches. The value of these resistors is typically about 100 .
The C2 capacitors are the ADC sampling capacitors and
typically have a capacitance of 16 pF.
AVDD
C1
D
R1 C2
AVDD
C1
D
R1 C2
08675-
021
Figure 27. Equivalent Analog Input Circuit Conversion Phase: Switches Open,
Track Phase: Switches Closed
For ac applications, removing high frequency components from
the analog input signal is recommended by using an RC low-
pass filter on the relevant analog input pins. In applications
where harmonic distortion and signal-to-noise ratio are critical,
the analog input should be driven from a low impedance
source. Large source impedances significantly affect the ac
performance of the ADC. This can necessitate the use of an
input buffer amplifier. The choice of the op amp is a function of
the particular application. Figure 28 and Figure 29 give an
example of an ADC front end.
08675-
022
ADuC7023
ADC0
10
0.01F
Figure 28. Buffering Single-Ended Differential Input
08675-
023
ADuC7023
ADC0
VREF
ADC1
Figure 29. Buffering Differential Inputs
When no amplifier is used to drive the analog input, limit the
source impedance to values lower than 1 k. The maximum
source impedance depends on the amount of total harmonic
distortion (THD) that can be tolerated. The THD increases as
the source impedance increases and the performance degrades.
DRIVING THE ANALOG INPUTS
Internal or external references can be used for the ADC. When
operating in differential mode, there are restrictions on the
common-mode input signal (VCM), which is dependent upon
the reference value and supply voltage used to ensure that the
signal remains within the supply rails. Table 27 gives some
calculated VCM minimum and VCM maximum values.
Table 27. VCM Ranges
AVDD
VREF
VCM Min
VCM Max
Signal Peak-to-Peak
3.3 V
2.5 V
1.25 V
2.05 V
2.5 V
2.048 V
1.024 V
2.276 V
2.048 V
1.25 V
0.75 V
2.55 V
1.25 V
3.0 V
2.5 V
1.25 V
1.75 V
2.5 V
2.048 V
1.024 V
1.976 V
2.048 V
1.25 V
0.75 V
2.25 V
1.25 V
CALIBRATION
By default, the factory-set values written to the ADC offset
(ADCOF) and gain coefficient registers (ADCGN) yield
optimum performance in terms of endpoint errors and linearity
for standalone operation of the part (see the Specifications
section). If system calibration is required, it is possible to
modify the default offset and gain coefficients to improve
endpoint errors, but note that any modification to the factory-
set ADCOF and ADCGN values can degrade ADC linearity
performance.
For system offset error correction, the ADC channel input stage
must be tied to AGND. A continuous software ADC conversion
loop must be implemented by modifying the value in ADCOF until
the ADC result (ADCDAT) reads Code 0 to Code 1. If the
ADCDAT value is greater than 1, ADCOF should be decremented
until ADCDAT reads Code 0 to Code 1. Offset error correction
is done digitally and has a resolution of 0.25 LSB and a range of
±3.125% of VREF.
For system gain error correction, the ADC channel input
stage must be tied to VREF. A continuous software ADC
conversion loop must be implemented to modify the value
in ADCGN until the ADCDAT reads Code 4094 to Code 4095.
If the ADCDAT value is less than 4094, ADCGN should be
incremented until ADCDAT reads Code 4094 to Code 4095.
Similar to the offset calibration, the gain calibration resolution
is 0.25 LSB with a range of ±3% of VREF.
TEMPERATURE SENSOR
The ADuC7023 provides a voltage output from an on-chip
band gap reference that is proportional to absolute temperature.
This voltage output can also be routed through the front-end
ADC multiplexer (effectively an additional ADC channel
input), facilitating an internal temperature sensor channel,
measuring die temperature.
An ADC temperature sensor conversion differs from a standard
ADC voltage. The ADC performance specifications do not
apply to the temperature sensor.
Chopping of the internal amplifier should be enabled using the
TSCON register. To enable this mode, the user must set Bit 0 of
TSCON. The user must also take two consecutive ADC readings
and average them in this mode.
Rev. E
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