Capacitance (pF)

1

10

100

1k

1

10

20

.

Frequency (Hz)

-18

-12

-6

0

6

12

18

10M

100M

1G

.

Figure 8-8. Frequency Response vs Capacitive

Load

8.3.1.4 Line Driver Headroom Model

The first step in a driver design is to compute the peak-to-peak output voltage from the target specifications. This

calculation is done using the following equations:

P =10

log

´

L

(1mW)

R

´

L

V

RMS

2

(2)

V

=

RMS

10

P

(1mW)

R

10

´

´

L

L

(3)

V =CrestFactor

V

=CF

V

P

RMS

RMS

´

´

(4)

V

=2

CF

V

LP

RMS

P

´

´

(5)

Consolidating Equation 2 through Equation 5 allows the required peak-to-peak voltage at the load function of the

crest factor, the load impedance, and the power in the load to be expressed. Thus:

V

=2

CF

LPP

´

´

10

P

(1mW)

R

10

´

´

L

L

(6)

The next step for the driver is to compute the individual amplifier output voltage and currents as a function of

changes. The peak current in the amplifier is given by:

±I =

P

1

´

2

1

n

2

V

´

LPP

´

(7)

OPA2675

SBOSAA5B – APRIL 2022 – REVISED SEPTEMBER 2022

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