ALD500R Ver la hoja de datos (PDF) - Advanced Linear Devices

Número de pieza

componentes Descripción

Fabricante

ALD500R

PRECISION INTEGRATING ANALOG PROCESSOR WITH PRECISION VOLTAGE REFERENCE

Advanced Linear Devices 

e. Very high resolution, high accuracy measurements

can be achieved simply and at very low cost.

An inherent benefit of the dual slope converter system is noise

immunity. The input noise spikes are integrated (averaged to

near zero) during the integration periods. Integrating ADCs

are immune to the large conversion errors that plague

successive approximation converters and other high resolution

converters and perform very well in high-noise environments.

The slow conversion speed of the integrating converter provides

inherent noise rejection with at least a 20dB/decade attenuation

rate. Interference signals with frequencies at integral multiples

of the integration period are, theoretically, completely removed.

Integrating converters often establish the integration period to

reject 50/60Hz line frequency interference signals.

The relationship of the integrate and deintegrate (charge

and discharge) of the integrating capacitor values are

shown below:

VINT = VX - (VIN . tINT / RINT . CINT)

(integrate cycle)

(1)

VX = VINT - (VREF . tDINT / RINT . CINT)

(deintegrate cycle)

(2)

Combining equations 1 and 2 results in:

VIN / VREF = -tDINT / tINT

(3)

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

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

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.

The Reference Voltage Deintegration Phase is initiated

immediately after tINT, within 1 clock cycle. During

ReferenceVoltage 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.

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

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

tDINT

VIN ≈ VFULL SCALE

VIN ≈ 1/2VFULL SCALE

Vx ≈ 0

tINT

tDINT

VINT = 4.1V MAX

AB

MICROCONTROLLER

(CONTROL LOGIC

+ COUNTER)

COUT

Figure 2. Basic Dual-Slope Converter

ALD500RAU/ALD500RA/ALD500R

Advanced Linear Devices

3

Share Link: