LTC6943

5

6943f

Test Circuit 1. Leakage Current Test

Common Mode Rejection Ratio (CMRR)

The LTC6943, when used as a differential to single-ended

converter rejects common mode signals and preserves

differential voltages (Figure 1). Unlike other techniques,

the LTC6943’s CMRR does not degrade with increasing

common mode voltage frequency. During the sampling

mode, the impedance of Pins 1, 2 (and 9, 10) should be

balanced, otherwise, common mode signals will appear

differentially. The value of the CMRR depends on the value

sampling frequency. Since the common mode voltages

are not sampled, the common mode signal frequency can

well exceed the sampling frequency without experiencing

aliasing phenomena. The CMRR of Figure 1 is measured

by shorting Pins 6 and 11 and by observing, with a

TEST CIRCUITS

Test Circuit 4. CMRR Test

6943 • TC04

CMRR = 20 LOG

()

BE LARGER THAN 0.0047µF, AND

THE SAMPLING CAPACITOR ACROSS

PINS 9 AND 10 SHOULD BE PLACED

OVER A SHIELD TIED TO PIN 8

+

+

11

12

10

9

8

67

1µF

1µF

CAPACITORS ARE

NOT ELECTROLYTIC

NOTE:

APPLICATIO S I FOR ATIO

Figure 1. Differential to Single-Ended Converter

6943 • TC01

(6, 11, 5, 16)

(7, 12, 4, 13)

(9, 10, 1, 2)

NOTE: TO OPEN SWITCHES,

S1 AND S3 PIN 14,

SHOULD BE CONNECTED

TO V–. TO OPEN S2, S4, THE

+

A

0V TO 10V

6943 • AI01

+

11

12

10

9

1/2 LTC6943

67

+

+

+

V+

6943 • TC03

3

V–

14

(TEST PIN)

IV

4

LTC6943

15

1

+

5

6943 • TC02

(6, 11, 5, 16)

(7, 12, 4, 13)

(9, 10, 1, 2)

100µA to 1mA

CURRENT SOURCE

+

A

VIN