9

®

OPA404

BIAS CURRENT CHANGE

vs COMMON-MODE VOLTAGE

The input bias currents of most popular BIFET operational

amplifiers are affected by common-mode voltage (Figure 4).

Higher input FET gate-to-drain voltage causes leakage and

ionization (bias) currents to increase. Due to its cascode

input stage, the extremely low bias current of the OPA404 is

not compromised by common-mode voltage.

APPLICATIONS CIRCUITS

Figures 5 through 11 are circuit diagrams of various appli-

cations for the OPA404.

In

Out

Zero

1M

Ω

2

3

1

6

7

5

Polypropylene

1µF

Gain = –100

V

Drift

≈ 0.05µV/°C

Zero Droop

≈ 1µV/s

Referred to Input

1/4

OPA404

100k

Ω

10k

Ω

100k

Ω

100

Ω

Operate

1/4

OPA404

–10

–5

0

+5

+10

–20

–10

0

10

20

30

40

50

60

70

80

LF155

OP-15/16/17

AD547

LF156/157

AD547

OPA404

LF156/157

T

mfg. published typical data

Common-Mode Voltage (VDC)

–15

+15

LF155

OPA404

FIGURE 4. Input Bias Current vs Common-Mode Voltage.

FIGURE 5. Auto-Zero Amplifier.

FIGURE 6. Low-Droop Positive Peak Detector.

Input

Output

6

7

5

2

3

1

10k

Ω

IN914

1M

Ω

2N4117

0.01µF Polstyrene

Droop

≈ 0.1mV/s

≈10pF

1/4

OPA404

1/4

OPA404

IN914

(1)

(1)

(1)

NOTE: (1) Reverse polarity for negative peak detection.