参数资料
型号: EVAL-ADUC7124QSPZ
厂商: Analog Devices Inc
文件页数: 40/108页
文件大小: 0K
描述: BOARD EVALUATION FOR ADUC7124
设计资源: EVAL-ADUC7124 Schematic
ADUC7124 Eval Brd Gerber Files
标准包装: 1
系列: MicroConverter® ADuC7xxx
类型: MCU
适用于相关产品: ADUC7124
所含物品:
Data Sheet
ADuC7124/ADuC7126
Rev. C | Page 37 of 108
ADC CIRCUIT OVERVIEW
The analog-to-digital converter is a fast, multichannel, 12-bit
ADC. It can operate from 2.7 V to 3.6 V supplies and is capable
of providing a throughput of up to 1 MSPS when the clock source
is 41.78 MHz. This block provides the user with a multichannel
multiplexer, a differential track-and-hold, an on-chip reference,
and an ADC.
The ADC consists of a 12-bit successive approximation con-
verter based around two capacitor DACs. Depending on the
input signal configuration, the ADC can operate in one of
three different modes.
Fully differential mode, for small and balanced signals
Single-ended mode, for any single-ended signals
Pseudo differential mode, for any single-ended signals,
taking advantage of the common-mode rejection offered
by the pseudo differential input
The converter accepts an analog input range of 0 V to VREF when
operating in single-ended or pseudo differential mode. In fully
differential mode, the input signal must be balanced around a
common-mode voltage (VCM) in the 0 V to AVDD range with a
maximum amplitude of 2 × VREF (see Figure 27).
09
12
3-
01
1
AVDD
VCM
0
2VREF
Figure 27. Examples of Balanced Signals in Fully Differential Mode
A high precision, low drift, factory calibrated, 2.5 V reference is
provided on chip. An external reference can also be connected as
described in the Band Gap Reference section.
Single or continuous conversion modes can be initiated in the
software. An external CONVSTART pin, an output generated from
the on-chip PLA, or a Timer0 or Timer1 overflow can also be
used to generate a repetitive trigger for ADC conversions.
A voltage output from an on-chip band gap reference propor-
tional to absolute temperature can also be routed through the
front-end ADC multiplexer, effectively an additional ADC channel
input. This facilitates an internal temperature sensor channel
that measures die temperature.
TRANSFER FUNCTION
Pseudo Differential and Single-Ended Modes
In pseudo differential or single-ended mode, the input range is
0 V to VREF. The output coding is straight binary in pseudo
differential and single-ended modes with
1 LSB = Full-Scale/4096, or
2.5 V/4096 = 0.61 mV, or
610 μV when VREF = 2.5 V
The ideal code transitions occur midway between successive
integer LSB values (that is, LSB, 32 LSB, 52 LSB, … ,
FS 3/2 LSB). The ideal input/output transfer characteristic
is shown in Figure 28.
09
12
3-
01
2
O
UT
P
UT
CO
DE
VOLTAGE INPUT
1111 1111 1111
1111 1111 1110
1111 1111 1101
1111 1111 1100
0000 0000 0011
1LSB
0V
+FS – 1LSB
0000 0000 0010
0000 0000 0001
0000 0000 0000
1LSB =
FULL-
SCALE
4096
Figure 28. ADC Transfer Function in Pseudo Differential or Single-Ended Mode
Fully Differential Mode
The amplitude of the differential signal is the difference between
the signals applied to the VIN+ and VIN– pins (that is, VIN+ – VIN–).
VIN+ is selected by the ADCCP register, and VIN is selected by
the ADCCN register. The maximum amplitude of the differential
signal is, therefore, –VREF to +VREF p-p (that is, 2 × VREF). This is
regardless of the common mode (CM). The common mode is
the average of the two signals, for example, (VIN+ + VIN–)/2, and
is, therefore, the voltage that the two inputs are centered on.
This results in the span of each input being CM ± VREF/2. This
voltage must be set up externally, and its range varies with VREF
(see the Driving the Analog Inputs section).
The output coding is twos complement in fully differential mode
with 1 LSB = 2 × VREF/4096, or 2 × 2.5 V/4096 = 1.22 mV when
VREF = 2.5 V. The output result is ±11 bits, but this is shifted by
one to the right. This allows the result in ADCDAT to be declared
as a signed integer when writing C code. The designed code
transitions occur midway between successive integer LSB values
(that is, LSB, 32 LSB, 52 LSB, … , FS 32 LSB). The ideal
input/output transfer characteristic is shown in Figure 29.
09
12
3-
0
13
O
U
T
P
UT
CO
DE
VOLTAGE INPUT (VIN+ – VIN–)
0 1111 1111 1110
0 1111 1111 1100
0 1111 1111 1010
0 0000 0000 0010
0 0000 0000 0000
1 1111 1111 1110
1 0000 0000 0100
1 0000 0000 0010
1 0000 0000 0000
–VREF + 1LSB
+VREF – 1LSB
0LSB
1LSB =
2 × VREF
4096
SIGN
BIT
Figure 29. ADC Transfer Function in Differential Mode
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