ALD500 데이터 시트보기 (PDF) - Advanced Linear Devices
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ALD500 Datasheet PDF : 11 Pages
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(integrate cycle)
VX = VINT - (VREF . tDINT / RINT . CINT)
(deintegrate cycle)
Combining equations 1 and 2 results in:
(1) Phase, internal analog switches connect VIN to the buffer
input where it is maintained for a fixed integration time period
(tINT). This fixed integration period is generally determined by
a digital counter controlled by a crystal oscillator. The
(2) application of VIN causes the integrator output to depart 0V at
a rate determined by VIN and a direction determined by the
polarity of VIN.
VIN / VREF = -tDINT / tINT
(3)
where:
Vx = An offset voltage used as starting voltage
VINT = Voltage change across CINT during tINT and
during tDINT (equal in magnitude)
VIN = Average, or an integrated, value of input voltage
to be measured during tINT (Constant VIN)
tINT = Fixed time period over which unknown voltage is
integrated
tDINT = Unknown time period over which a known
reference voltage is integrated
VREF = Reference Voltage
CINT = Integrating Capacitor value
RINT = Integrating Resistor value
Actual data conversion is accomplished in two phases: Input
Signal Integration Phase and Reference Voltage Deintegration
Phase.
The integrator output is initialized to 0V prior to the start of
Input Signal Integration Phase. During Input Signal Integration
The Reference Voltage Deintegration Phase is initiated
immediately after tINT, within 1 clock cycle. During Reference
Voltage Deintegration Phase, internal analog switches connect
a reference voltage having a polarity opposite that of VIN to
the integrator input. Simultaneously the same digital counter
controlled by the same crystal oscillator used above is used to
start counting clock pulses. The Reference Voltage
Deintegration Phase is maintained until the comparator output
inside the dual slope analog processor changes state, indicating
the integrator has returned to 0V. At that point the digital
counter is stopped. The Deintegration time period (tDINT), as
measured by the digital counter, is directly proportional to the
magnitude of the applied input voltage.
After the digital counter value has been read, the digital
counter, the integrator, and the auto zero capacitor are all
reset to zero through an Integrator Zero Phase and an Auto
Zero Phase so that the next conversion can begin again. In
practice, this process is usually automated so that analog-to-
digital conversion is continuously updated. The digital control
is handled by a microprocessor or a dedicated logic controller.
The output, in the form of a binary serial word, is read by a
microprocessor or a display adapter when desired.
ANALOG
INPUT
(VIN)
VOLTAGE
REFERENCE
S1
REF
SWITCHES
CINT
RINT
INTEGRATOR
-
+
VINT
+
-
COMPARATOR
POLARITY
DETECTION
SWITCH DRIVER
PHASE
CONTROL
POLARITY CONTROL
CONTROL
LOGIC
COUT
tDINT
VIN ≈ VFULL SCALE
VIN ≈ 1/2 VFULL SCALE
VX ≈ 0
tINT
tDINT
VINT = 4.1V MAX
AB
MICROCONTROLLER
(CONTROL LOGIC
+ COUNTER)
Figure 2. Basic Dual-Slope Converter
Figure 2. Basic Dual-Slope Converter
ALD500AU/ALD500A/ALD500
Advanced Linear Devices
3
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