TC534CPL データシートの表示（PDF） - TelCom Semiconductor, Inc

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TC534CPL

5V PRECISION DATA ACQUISITION SUBSYSTEMS

TelCom Semiconductor, Inc 

TC530

TC534

5V PRECISION DATA ACQUISITION

SUBSYSTEMS

Conversion

Phase

AZ

INT

Data to Serial

Port Transmit

Register

EOC

Updated Data

Ready

tDR

DINT

IZ

AZ

Updated Data

Ready

Figure 2. A/D Converter Timing

DETAILED DESCRIPTION

Dual Slope Integrating Converter

The TC530/534 dual slope converter operates by inte-

grating the input signal for a fixed time period, then applying

an opposite polarity reference voltage while timing the

period (counting clocks pulses) for the integrator output to

cross 0V (deintegrating). The resulting count is read as

conversion data.

A simple mathematical expression that describes dual

slope conversion is:

(1) Integrate Voltage = Deintegrate Voltage

∫ ∫ (2) 1/RINTCINT

tINT

VIN(t)dt = 1/RINTCINT

0

tDINT

VREF

0

from which:

Another inherent benefit is noise immunity. Input noise

spikes are integrated (or averaged to zero) during the

integration period. The integrating converter has a noise

immunity with an attenuation rate of at least –20dB per

decade. Interference signals with frequencies at integral

multiples of the integration period are, for the most part,

completely removed. For this reason, the integration period

of the converter is often established to reject 50/60Hz line

noise. The ability to reject such noise is shown by the plot of

Figure 3.

In addition to the two phases required for dual slope

measurement (Integrate and Deintegrate), the TC530/534

performs two additional adjustments to minimize measure-

ment error due to system offset voltages. The resulting four

internal operations (conversion phases) performed each

measurement cycle are: Auto Zero (AZ), Integrator Output

Zero (IZ), Input Integrate (INT) and Reference Deintegrate

(DINT). The AZ and IZ phases compensate for system offset

errors and the INT and DINT phases perform the actual A/D

conversion.

[ ] [ ] (3) (VIN)

(tINT)

(RINT)(CINT)

= (VREF)

(tDINT)

(RINT)(CINT)

and therefore:

[ ] (4) VIN = VREF

tDINT

tINT

where: VREF = Reference Voltage

tINT = Integrate Time

tDINT = Reference Voltage Deintegrate Time

Inspection of equation (4) shows dual slope converter

accuracy is unrelated to integrating resistor and capacitor

values, as long as they are stable throughout the measure-

ment cycle. This measurement technique is inherently

ratiometric (i.e., the ratio between the tINT and tDINT times is

equal to the ratio between VIN and VREF).

3-54

30

T = MEASUREMENT

PERIOD

20

10

0

0.1/T

1/T

INPUT FREQUENCY

10/T

Figure 3. Integrating Converter Normal Mode Rejection

TELCOM SEMICONDUCTOR, INC.

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