LOG112, 2112

10

SBOS246C

www.ti.com

FIGURE 11. Single +5V Power-Supply Operation.

14

1

5

10

6

9

1

2

35

4

–5V

1

µF

LOG112

1

µF

I

1

I

2

V

LOGOUT

C

C

1

µF

Single Supply +5V

NOTE: (1) TPS60402DBV

negative charge pump.

FIGURE 10. Absorbance Measurement.

I

2

I

1

14

1

9

10

5

V

LOGOUT

6

V+

V–

C

C

LOG112

D

2

D

1

Sample

λ

1

λ

λ

1

Light

Source

DATA COMPRESSION

In many applications, the compressive effects of the logarith-

mic transfer function are useful. For example, a LOG112

preceding a 12-bit A/D converter can produce the dynamic

range equivalent to a 20-bit converter.

OPERATION ON SINGLE SUPPLY

Many applications do not have the dual supplies required to

operate the LOG112 and LOG2112. Figure 11 shows the

LOG112 and LOG2112 configured for operation with a single

+5V supply.

MEASURING AVALANCHE PHOTODIODE CURRENT

The wide dynamic range of the LOG112 and LOG2112 is

useful for measuring avalanche photodiode current (APD), as

shown in Figure 12.

FIGURE 12. High-Side Shunt for APD Measures 3 Decades of APD Current.

A

1

–5V

SO-14

911

13

LOG112

Q

1

2

Q

2

I

OUT

I

10

3

4

10k

Ω

Receiver

Irx = 1

µA to 1mA

I-to-V

Converter

APD

10Gbits/sec

16.7k

Ω

C

C

A

2

A

3

V

I

SHUNT

500

Ω

5k

Ω

5k

Ω

+15V to +60V

+5V

INA168

SOT23-5

+5V

1

1

14

8

6

5

7

100

µA

25k

Ω

V

REF