TLV2352, TLV2352Y

LinCMOS

™ DUAL LOW-VOLTAGE DIFFERENTIAL COMPARATORS

SLCS011B – MAY 1992 – REVISED MARCH 1999

12

POST OFFICE BOX 655303

PARAMETER MEASUREMENT INFORMATION

Figure 10 illustrates a practical circuit for direct dc measurement of input offset voltage that does not bias the

comparator in the linear region. The circuit consists of a switching-mode servo loop in which U1a generates a

triangular waveform of approximately 20-mV amplitude. U1b acts as a buffer with C2 and R4 removing any residual

dc offset. The signal is then applied to the inverting input of the comparator under test while the noninverting input

is driven by the output of the integrator formed by U1c through the voltage divider formed by R9 and R10. The loop

reaches a stable operating point when the output of the comparator under test has a duty cycle of exactly 50%, which

can only occur when the incoming triangle wave is sliced symmetrically or when the voltage at the noninverting input

exactly equals the input offset voltage.

Voltage dividers R9 and R10 provide a step up of the input offset voltage by a factor of 100 to make measurement

easier. The values of R5, R8, R9, and R10 can significantly influence the accuracy of the reading; therefore, it is

suggested that their tolerance level be 1% or lower.

Measuring the extremely low values of input current requires isolation from all other sources of leakage current and

compensation for the leakage of the test socket and board. With a good picoammeter, the socket and board leakage

can be measured with no device in the socket. Subsequently, this open-socket leakage value can be subtracted from

the measurement obtained with a device in the socket to obtain the actual input current of the device.

–

+

DUT

VDD

+

–

–

+

–

+

C2

1

µF

R4

47 k

Ω

R5

1.8 k

Ω, 1%

C3

0.68

µF

U1c 1/4

TLC2344

U1b 1/4

TLC2344

U1a 1/4

TLC2344

R7

1 M

Ω

R8

1.8 k

Ω, 1%

R9

10 k

Ω, 1%

R1

240 k

Ω

R2

10 k

Ω

C1

0.1

µF

R3

100

Ω

C4

0.1

µF

Integrator

R10

100

Ω, 1%

Buffer

Triangle

Generator

VIO

(

×100)

R6

5.1 k

Ω

Figure 10. Circuit for Input Offset Voltage Measurement