ML2008, ML2009
TYPICAL PERFORMANCE CURVES
(Continued)
100
ATTEN: V
IN
= 8dBm
GAIN: V
IN
= 8dBm/GAIN SETTING
1kHZ
GAIN ERROR
(dB)
0.1
.08
.06
.04
.02
0
–.02
–.04
90
C
MSG
S/N (DB)
80
70
60
50
–.06
–.08
40
–24
–18
–12
–6
0
6
12
18
24
–1.0
–24
–18
–12
–6
0
6
12
18
24
GAIN SETTING (dB)
GAIN SETTING (dB)
Figure 6. C
MSG
S/N vs Gain Setting
80
V
IN
= 1kH
z
70
60
S/N + D (dB)
50
40
30
V
IN
= 50kH
z
20 ATTEN: V = 2V
IN
RMS
GAIN: V
IN
= 2V
RMS
/GAIN SETTING
10
–24
–18
–12
–6
0
30
V
IN
= 20kHz
S/N + D (dB)
70
Figure 7. Gain Error vs Gain Setting
80
V
IN
= 1kHz
V
IN
= 20kHz
60
V
IN
= 50kHz
50
40
ATTEN: V
IN
= 0.5V
RMS
GAIN: V
IN
= 0.5V
RMS
/GAIN SETTING
–18
–12
–6
0
6
12
18
24
6
12
18
24
20
–24
GAIN SETTING (dB)
GAIN SETTING (dB)
Figure 8. S/N +D vs Gain Setting (V
IN
/V
OUT
= 2V
RMS
)
Figure 9. S/N +D vs Gain Setting (V
IN
/V
OUT
= 0.5V
RMS
)
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
The analog input, V
IN
, goes directly into the op amp input
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
6
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
