ALD500RAU-10SE データシートの表示（PDF） - Advanced Linear Devices

部品番号

コンポーネント説明

メーカー

ALD500RAU-10SE

PRECISION INTEGRATING ANALOG PROCESSOR WITH PRECISION VOLTAGE REFERENCE

Advanced Linear Devices 

FIGURE 1. ALD500R Functional Block Diagram

RREF = 100KΩ

CB = 0.1µF

V+IN

(14)

CREF

RINT

CINT

V+REF

(12)

V-REF

(11)

C+REF

RREF

C-REF

BUF

(8)

(7)

(5)

REFINT

SWIN

SWR SWR

-

Buffer

+

SW-R SW+R

CAZ

CAZ

(4)

CINT

(2)

Integrator

-

+

+

Comp1

-

SWAz

AGND

(6)

V-IN

(13)

SWIN

SW+R

SW-R

SWG

SWS SWAZ

REF

Control

Bias

Analog

Switch

Control

Signals

-

Comp2

+

Level

Shift

Polarity

Detection

Phase

Decoding

Logic

COUT

(17)

DGND

(18)

VSS VDD N/C N/C

(3) (19) (10) (9)

IB CB

CS

(20)

(1)

A

B

(15) (16)

Control Logic

GENERAL DESCRIPTION

The ALD500RAU/ALD500RA/ALD500R are integrating

dual slope analog processors, designed to operate on ±5V

power supplies for building precision analog-to-digital

converters. The ALD500RAU/ALD500RA/ALD500R

feature specifications suitable for 18 bit/17 bit/16 bit

resolution conversion, respectively. Together with three

capacitors, two resistors, and a digital controller, a precision

Analog to Digital converter with auto zero can be

implemented. The digital controller can be implemented

by an external microcontroller, under either hardware

(fixed logic) or software control. For ultra high resolution

applications, up to 23 bit conversion can be implemented

with an appropriate digital controller and software.

The ALD500R series of analog processors accept

differential inputs and the external digital controller first

counts the number of pulses at a fixed clock rate that a

capacitor requires to integrate against an unknown analog

input voltage, then counts the number of pulses required

to deintegrate the capacitor against a known internal

reference voltage. This unknown analog voltage can then

be converted by the microcontroller to a digital word, which

is translated into a high resolution number, representing

an accurate reading. This reading, when ratioed against

the reference voltage, yields an accurate, absolute voltage

measurement reading.

The ALD500R analog processors consist of on-chip digital

control circuitry to accept control inputs, integrating buffer

amplifiers, analog switches, and voltage comparators and

a highly accurate, ultra-stable voltage reference. It

functions in four operating modes, or phases, namely auto

zero, integrate, deintegrate, and integrator zero phases.

At the end of a conversion, the comparator output goes

from high to low when the integrator crosses zero during

deintegration. ALD500R analog processors also provide

direct logic interface to CMOS logic families.

GENERAL THEORY OF OPERATION

Dual-Slope Conversion Principles of Operation

The basic principle of dual-slope integrating analog to digital

converter is simple and straightforward. A capacitor, CINT, is

charged with the integrator from a starting voltage, VX, for a

fixed period of time at a rate determined by the value of an

unknown input voltage, which is the subject of measurement.

Then the capacitor is discharged at a fixed rate, based on an

external reference voltage, back to VX where the discharge

time, or deintegration time, is measured precisely. Both the

integration time and deintegration time are measured by a

digital counter controlled by a crystal oscillator. It can be

demonstrated that the unknown input voltage is determined

by the ratio of the deintegration time and integration time, and

is directly proportional to the magnitude of the external reference

voltage.

The major advantages of a dual-slope converter are:

a. Accuracy is not dependent on absolute values of

integration time tINT and deintegration time tDINT, but is

dependent on their relative ratios. Long-term clock frequency

variations will not affect the accuracy. A standard crystal

controlled clock running digital counters is adequate to generate

very high accuracies.

b. Accuracy is not dependent on the absolute values of

RINT and CINT, as long as the component values do not vary

through a conversion cycle, which typically lasts less than 1

second.

c. Offset voltage values of the analog components, such

as VX, are cancelled out and do not affect accuracy.

d. Accuracy of the system depends mainly on the accuracy

and the stability of the voltage reference value.

2

Advanced Linear Devices

ALD500RAU/ALD500RA/ALD500R

Share Link: