Datasheet
W0004-01
(a) Single-Ended Input at V
CNTLP
(b) Differential Inputs at V and V
CNTLP CNTLM
TGC Gain
V = 0V
CNTLM
V
CNTLP
1.5V
XdB
X+40dB
TGC Gain
0V
V
CNTLM
V
CNTLP
XdB
X+40dB
1.5V
0.75V
AFE5808A
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SLOS729B –OCTOBER 2011–REVISED APRIL 2012
LNA Gain Switch Response
The LNA gain is programmable through SPI. The gain switching time depends on the SPI speed as well as the
LNA gain response time. During the switching, glitches might occur and they can appear as artifacts in images.
LNA gain switching in a single imaging line may not be preferred, although digital signal processing might be
used here for glitch suppression.
VOLTAGE-CONTROLLED-ATTENUATOR
The attenuator in the AFE5808A is controlled by a pair of differential control inputs, the V
CNTLM/P
pins. The
differential control voltage spans from 0 V to 1.5 V. This control voltage varies the attenuation of the attenuator
based on its linear-in-dB characteristic. Its maximum attenuation (minimum channel gain) appears at V
CNTLP
-
V
CNTLM
= 1.5 V, and minimum attenuation (maximum channel gain) occurs at V
CNTLP
-V
CNTLM
= 0. The typical gain
range is 40 dB and remains constant, independent of the PGA setting.
When only single-ended V
CNTL
signal is available, this 1.5Vpp signal can be applied on the V
CNTLP
pin with the
V
CNTLM
pin connected to ground. As shown in Figure 86, TGC gain curve is inversely proportional to the V
CNTLP
-
V
CNTLM
.
Figure 86. V
CNTLP
and V
CNTLM
Configurations
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