Datasheet

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
1MΩ
2
3
1
6
7
5
Polypropylene
1µF
Gain = –100
V
OS
< 10µV
Drift ≈ 0.05µV/°C
Zero Droop ≈ 1µV/s
Referred to Input
1/4
OPA404
100kΩ
10kΩ
100kΩ
100Ω
Operate
1/4
OPA404
–10 –5 0 +5 +10
–20
–10
0
10
20
30
40
50
60
70
80
Input Bias Current (pA)
LF155

OP-15/16/17
AD547
LF156/157
AD547
OPA404
LF156/157
T
A
= +25°C; curves taken from 
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
10kΩ

IN914
1MΩ
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.