ML2008, ML2009

6

0.1

.08

.06

.04

.02

0

–.02

–.04

–.06

–.08

–1.0

–24

GAIN SETTING (dB)

–18

–12

–6

0

6

12

18

24

80

70

60

50

40

30

20

10

–24

GAIN SETTING (dB)

–18

–12

–6

0

6

12

18

24

80

70

60

50

40

30

20

GAIN SETTING (dB)

0

6

12

18

24

–24

–18

–12

–6

Figure 7. Gain Error vs Gain Setting

GAIN SETTING (dB)

0

6

12

18

24

100

90

80

70

60

50

40

1kHZ

–6

–12

–18

–24

1.0 FUNCTIONAL DESCRIPTION

The ML2008, ML2009 consists of a coarse gain stage, a

fine gain stage, an output buffer, and a

µP compatible

parallel digital interface.

1.1 Gain Stages

in the coarse gain stage. The coarse gain stage has a gain

range of 0 to 22.5dB in 1.5dB steps.

The fine gain stage is cascaded onto the coarse section.

The fine gain stage has a gain range of 0 to 1.5dB in 0.1dB

steps.

Both stages can be programmed for either gain or

attenuation, thus doubling the effective gain range.

The logarithmic steps in each gains stage are generated by

placing the input signal across a resistor string of 16 series

resistors. Analog switches allow the voltage to be tapped

from the resistor string at 16 points. The resistors are sized

such that each output voltage is at the proper logarithmic

ratio relative to the input signal at the top of the string.

Attenuation is implemented by using the resistor string as

a simple voltage divider, and gain is implemented by

using the resistor string as a feedback resistor around an

internal op amp.

1.2 Gain Settings

Since the coarse and fine gain stages are cascaded, their

gains can be summed logarithmically. Thus, any gain from

–24dB to +24dB in 0.1dB steps can be obtained by

combining the coarse and fine gain setting to yield the