AD603

REV. C

–7–

31.07dB

–42.14dB

GPOS

GNEG

31.07dB

–42.14dB

GPOS

GNEG

–40.00dB

–51.07dB

–8.93dB

INPUT

0dB

A1

A2

OUTPUT

–20dB

a.

31.07dB

–42.14dB

GPOS

GNEG

31.07dB

0dB

GPOS

GNEG

0dB

–11.07dB

31.07dB

INPUT

0dB

OUTPUT

20dB

b.

31.07dB

–2.14dB

GPOS

GNEG

31.07dB

0dB

GPOS

GNEG

0dB

–28.93dB

31.07dB

INPUT

0dB

OUTPUT

60dB

c.

Figure 6. AD603 Gain Control Input Calculations for Sequential Control Operation

+31.07dB

+10dB

A1

A2

+31.07dB

+28.96dB

–11.07dB

–11.07dB

0.473

1.526

–8.93dB

*

*

0

0.5

1.0

1.50

2.0

–20

0

20

40

60

62.14

–22.14

GAIN

(dB)

Figure 7. Explanation of Offset Calibration for Sequential

Control

thus the gain of A1 is –8.93 dB (recall that the gain of each indi-

vidual amplifier in the maximum-bandwidth mode is –10 dB

–1.908 V so the gain of A2 is “pinned” at –11.07 dB. The over-

all gain is thus –20 dB. This situation is shown in Figure 6a.

which sets the gain of A1 to at nearly its maximum value of

A2’s gain at nearly its minimum value –11.07 dB. Close analysis

shows that the degree to which neither AD603 is completely

pushed to its maximum or minimum gain exactly cancels in the

overall gain, which is now +20 dB. This is depicted in Figure 6b.

that of A2 is near its maximum value of 28.93 dB, resulting in

an overall gain of 60 dB (see Figure 6c). This mode of operation

is further clarified by Figure 8, which is a plot of the separate

gains of A1 and A2 and the overall gain versus the control voltage.

Figure 9 is a plot of the gain error of the cascaded amplifiers versus

the control voltage. Figure 10 is a plot of the gain error of the

cascaded stages versus the control voltages.

70

–30

–0.2

2.2

0.2

0.6

0.1

1.4

1.8

60

30

0

–10

–20

50

40

20

10

COMBINED

A1

A2

Figure 8. Plot of Separate and Overall Gains in Sequential

Control