7.2.5 Data Compression

In many applications, the compressive effects of the logarithmic transfer function are useful. For example, a

LOG114 preceding a 12-bit ADC can produce the dynamic range equivalent to a 20-bit converter (like the

ADS7818 or ADS7834).

7.2.6 3.3V Operation

For systems with only a 3.3V power supply, the TPS60241 zero-ripple switched cap buck-boost 2.7V to 5.5V

input to 5V output converter may be used to generate a 5V supply for the LOG114 (see Figure 7-12).

LOG114

TPS60241

V

IN

C

1+

C

1-

GND

V

OUT

C

2+

C

2-

EN

1 μF

1 μF

1 μF

I

1

I

2

1 μF

3.3V

V+

V–

V

LOGOUT

5V

Figure 7-12. Creating a 5V Supply from a 3.3V Supply

Likewise, the TPS6040 negative charge pump may be connected to the 5V output of the TPS60241 to generate

a −5V supply to create a ±5V supply for the LOG114 (see Figure 7-13).

1 μF

LOG114

TPS60241

TPS60400

C

FLY-

C

FLY+

IN

OUT

GND

1 μF

1 μF

-5V

V

IN

C

1+

C

1-

GND

V

OUT

C

2+

C

2-

EN

1 μF

1 μF

1 μF

1 μF

I

1

I

2

1 μF

3.3V

V+

5V

V–

-5V

V

LOGOUT

Figure 7-13. Creating a ±5V Supply from a 3.3V Supply

7.2.7 Erbium-Doped Fiber Optic Amplifier (EDFA)

The LOG114 was designed for optical networking systems. Figure 7-14 shows a block diagram of the LOG114 in

a typical EDFA application. This application uses two log amps to measure the optical input and output power of

the amplifier. A difference amplifier subtracts the log output signals of both log amps and applies an error voltage

to the proportional-integral-derivative (PID) controller. The controller output adjusts a voltage-controlled current

source (VCCS), which then drives the power op amp and pump laser. The desired optical gain is achieved when

the error voltage at the PID is zero.

LOG114

SBOS301B – MAY 2004 – REVISED MARCH 2025

www.ti.com

24

Submit Document Feedback

Copyright © 2025 Texas Instruments Incorporated

Product Folder Links: LOG114