9

LT1055/LT1056

Phase Reversal Protection

Most industry standard JFET input op amps (e.g., LF155/

LF156, LF351, LF411, OP15/16) exhibit phase reversal at

the output when the negitive common-mode limit at the

input is exceeded (i.e., from –12V to –15V with

±15V

supplies). This can cause lock-up in servo systems. As

shown below, the LT1055/LT1056 does not have this

problem due to unique phase reversal protection circuitry

(Q1 on simplified schematic).

0.5ms/DIV

0.5ms/DIV

0.5ms/DIV

LT1055/56 AI06

LT1055/56 AI07

LT1055/56 AI08

†

Exponential Voltage-to-Frequency Converter for Music Synthesizers

INPUT

0V TO 10V

LT1055/56 TA03

–

+

11.3k*

EXPONENT

TRIM

2500

Ω*

562

Ω*

3.57k*

ZERO TRIM

15V

500k

500

Ω*

4.7k

1.1k

10k*

3k

10k*

1k*

1k*

4.7k

2

3

4

5

6

–15V

–15V

7

LT1055

15V

500pF

POLYSTYRENE

6

2

3

15V

7

LM301A

15V

6

8

2N3906

2N3904

SAWTOOTH

OUTPUT

LM329

0.01µF

1

4

2

3

1

1N148

13

14

15 2.2k

9

7

8

33

Ω

TEMPERATURE CONTROL LOOP

SCALE FACTOR

1V IN OCTAVE OUT

*1% METAL FILM RESISTOR

PIN NUMBERED TRANSISTORS = CA3096 ARRAY

–

+

LT1055 and LT1056, please see the LTC1043

data sheet and Application Note 3.

Voltage Follower with Input Exceeding the Negative

Common-Mode Range

–

+

2k

–15V

15V

OUTPUT

2

3

4

INPUT

±15V

SINE WAVE

7

6

LT1055/56

LT1055/56 AI05

Output

LT1055/LT1056

Output

(LF155/LF56, LF441, OP-15/OP-16)

Input