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
AFE5808
www.ti.com SLOS688C –SEPTEMBER 2010–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 AFE5808 is controlled by a pair of differential control inputs, the VCNTLM/P pins. The
differential control voltage spans from 0V to 1.5V. This control voltage varies the attenuation of the attenuator
based on its linear-in-dB characteristic. Its maximum attenuation (minimum channel gain) appears at VCNTLP -
VCNTLM= 1.5V, and minimum attenuation (maximum channel gain) occurs at VCNTLP- VCNTLM = 0. The
typical gain range is 40dB and remains constant, independent of the PGA setting.
When only single-ended VCNTL signal is available, this 1.5V
PP
signal can be applied on the VCNTLP pin with
the VCNTLM pin connected to ground. As shown in Figure 85, the TGC gain curve is inversely proportional to
the V
CNTLP
-V
CNTLM
.
Figure 85. V
CNTLP
and V
CNTLM
Configurations
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