07/07/06

10

ES51999

4 3/4 and 5 3/4 A/D AUTO

∫

×

×

×

=

×

INT

T

DINT

REF

IN

T

V

C

Buf

dt

t

V

C

Buf

0

int

1

)

(

int

1

where,

)

(t

V

IN

= input signal

REF

V

= reference voltage

INT

T

= integration time (fixed)

DINT

T

= de-integration time (proportional to

)

(t

V

IN

)

If

)

(t

V

IN

is a constant, we can rewrite above equation:

IN

REF

INT

DINT

V

V

T

T

×

=

Besides the INT phase and DINT phase, ES51999 exploits auto zero (AZ) phase and zero

integration (ZI) phase to achieve accurate measurement. In AZ phase, the system offset is

stored. The offset error will be eliminated in DINT phase. Thus a higher accuracy could

be obtained. In ZI phase, the internal status will be recovered quickly to that of zero input.

Thus the succeeding measurements won’t be disturbed by current measurement

especially in case of overload.

input

signal

reference

voltage

Buf

Raz

Cint

integrator

output

integration

time

input signal > 0

Fixed

integration

time

Variable

deintegration

time

integration

time

input signal < 0

Fixed

integration

time

Variable

deintegration

time

fixed slope

fixed slope

different

input

different

input

Figure 2.1 the structure of dual-slope integrator and its output waveform.

As mentioned above, the measurement cycle of ES51999 contains four phases:

(1) auto zero phase (AZ)

(2) input signal integration phase (INT)

(3) reference voltage integration phase (DINT)