Frequency (Hz)

-30

-27

-24

-21

-18

-15

-12

-9

-6

-3

0

3

6

9

1

10

100

1k

10k 100k 1M

10M 100M 1G

10G

Cross-Over

Frequency

Region

D004

High Frequency Region

Low Frequency Region

Figure 8-14. Low, Cross-Over, High Frequency Region

The transfer function of the composite loop in Mode B can be split into the following 3 frequency regions:

1. Low Frequency Region: the gain of the composite loop in the low-frequency region is α/β (determined by

α and β network). In the low-frequency region the 330 pF input capacitor presents a high-impedance in the

Main path, causing the signal to flow through the precision amplifier and the In_Aux pin. This region spans

bandwidth and other parasitic capacitance of the BUF802.

2. High Frequency Region: in the high-frequency region the precision amplifier and the Auxiliary path run out

of bandwidth. The gain of the composite loop in this region is determined solely by the BUF802s Main path

the pole resulting from the 330 pF series capacitor and the 10 MΩ resistor on the In_Bias pin.

3. Cross-over Frequency Region: the Main path and Auxiliary path work in conjunction to determine the gain

in the crossover region. To maintain a flat frequency response in this region the following conditions have to

be met :

a. α/β = G

A detailed analysis of discrete component selection to achieve a flat frequency response is discussed further

in the Section 9.1.

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BUF802

SBOS998 – JUNE 2021

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