a) Single-Pole Filter

b) Second-Order, Sallen-Key Filter

A1

A2

Single-Pole Filter

Capacitor

+2.7 V to +18 V

5 kW

5 kW

96 kW

R

L

PRE OUT

BUF IN

GND

Output

IN-

IN+

V+

Load

Supply

R

S

A1

A2

Second-Order, Sallen-Key Filter Connection

+2.7 V to +18 V

C

FILT

C

FILT

5 kW

5 kW

96 kW

R

L

PRE OUT

BUF IN

GND

Output

IN-

IN+

V+

Load

Supply

R

S

R

S

13

INA901-SP

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SBOS938C – OCTOBER 2018 – REVISED JUNE 2020

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7.4 Device Functional Modes

7.4.1 First- or Second-Order Filtering

The output of the INA901-SP is accurate within the output voltage swing range set by the power-supply pin, V+.

The INA901-SP readily enables the inclusion of filtering between the preamp output and buffer input. Single-pole

filtering can be accomplished with a single capacitor because of the 96-k

Ω output impedance at PRE OUT on pin

3, as shown in Figure 16a.

The INA901-SP readily lends itself to second-order Sallen-Key configurations, as shown in Figure 16b. When

designing these configurations consider that the PRE OUT 96-k

Ω output impedance exhibits an initial variation of

±30% with the addition of a –2200-ppm/°C temperature coefficient.

NOTE: Remember to use the appropriate buffer gain = 2 when designing Sallen-Key configurations.

Figure 16. The INA901-SP Can Be Easily Connected for First- or Second-Order Filtering

This section addresses the accuracy of these specific operating regions: