Data Sheet

ADA4352-2

analog.com

Rev 0

37 of 47

RC Tolerancing and Effect of External RC Filter

This external RC filter also adds more control to the step response for the most peaked 315 Ω gain condition. The

following step responses assume an REXT = 200 Ω, CEXT = 180 pF, as used previously, a 0.5 V bias at +IN, CDof 10 pF,

and the part configured in the 315 Ω gain setting. The 1 V output step response in Figure 76 shows how the external

RC filter smooths the PGTIA ringing response.

Figure 76. Simulated (Left) and Measured (Right) 1 V Output Step at the Nominal 315 Ω Gain Setting at both VOUT and after the

External RC Filter

The three groups of curves in Figure 77 show the effects of extremes of component tolerance on step response.

Here, the minimum RF0 and CF0 values are used together, then the nominal values, and then the maximum RF0 and

CF0 values. All curves in Figure 77 were produced with the same input current, which would result in a 1 V output

step using a nominal RF0 = 315 Ω gain setting. The two extremes settle to a lower and higher final value, but all show

the same settling behavior after the external RC filter.

Figure 77. Simulated 1 V Output Step with Internal RC Tolerancing Extremes at the Nominal 315 Ω Gain Setting, with and

without External RC Filter

TIME (µs)

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

REXT = 200Ω

CEXT = 180pF

UNFILTERED

FILTERED

0.25

0.50

0.75

1.00

1.25

1.50

1.75

UNFILTERED

FILTERED

TIME (µs)

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

0.25

0.50

0.75

1.00

1.25

1.50

1.75

REXT = 200Ω

CEXT = 180pF

REXT = 200Ω

CEXT = 180pF

MINIMUM

MINIMUM FILTERED

NOMINAL

NOMINAL FILTERED

MAXIMUM

MAXIMUM FILTERED

TIME (µs)

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

0.25

0.50

0.75

1.00

1.25

1.50

1.75