Supported Configurations; Analog Front-End - Analog Devices EVAL-AD4080-FMCZ User Manual

User Guide

SUPPORTED CONFIGURATIONS

The following sections describe the hardware and software configu-
rations that the EVAL-AD4080-FMCZ supports.

ANALOG FRONT-END

Stage 1 Bypass
Stage 1 can be optionally bypassed to allow direct drive of the
second stage (FDA) from the SMA connectors.
To bypass Stage 1, do the following:
Remove R4, R6, R66 and R114 to disconnect the Stage 1
►
amplifiers from the stage input and output.
Populate R52 and R106 with 0 Ω resistors to create the bypass
►
path.
Close Switch 1 and Switch 2 from the Switch Array S1 (see
►
3) to power down the now unused U1 and U2 amplifiers.
Stage 1 Gain
Stage 1 amplifiers are arranged for unity gain by default; however,
this gain can be changed to a noninverting gain configuration.
To set the desired gain choose a feedback resistance (R
Gain = 1 +
resistance (R ) ratio according to the following equation:
R FB
G
R G
The necessary changes follow:
Change the R8 and R9 feedback resistors for a value of R
►
Populate R5 and R7 with a value of R
►
Populate 0 Ω R29 and R78 resistors.
►
For the JP7 and JP14 solder links, link Pad 1 to Pad 2.
►
Stage 1 Filtering
A differential, first-order, RC filter can be implemented at the input
of Stage 1 to bandwidth limit and reduce noise.
To obtain the desired 3 dB cutoff frequency sett values to the
frequency capacitance (C ) and frequency resistance (R
F
f =
the following:
1
3dB
2πR F C F
The necessary changes follow:
Change R4 and R6 to a R
►
F
Populate C67 and C79 with a C
►
In addition to the RC filter (or instead of), the C7 and C8 capacitors
across the feedback networks can be populated for further filtering.
analog.com
) to gain
FB
.
G
) so that
F
value.
value.
F
Stage 1: Alternative Input Signal Sources
Differential Signal Source
In the default board configuration, the signal chain input (that is,
Stage 1) is designed to be driven by a fully differential signal source
with 0 V common mode applied at the SMA inputs (INP and INM).
Because the default total gain of the signal chain is 1 by default, an
amplitude of 6 V p-p in the differential signal results in a full-scale
measurement at the ADC (−3 V to +3 V).
Note that the tight common-mode input requirement for the
(1.5 V ± 50 mV) does not apply to the signal at the input of the
board because the
common mode independently of the common mode at the input.
Table
Single-Ended Input Source
A single-ended (ground referenced) AC signal can be fed to one of
the EVAL-AD4080-FMCZ inputs (for example, INP), while the other
input is grounded. An amplitude of 6 V p-p results in a full-scale
measurement at the ADC (−3 V to +3 V).
When a single-ended signal source is applied at INP, the U2 amplifi-
er that buffers the other input (INM) can be optionally disabled and
bypassed. The necessary changes to do this follow:
Remove R6 and R114 to disconnect the amplifier input and
(1) ►
output from the circuit.
Populate R106 with a 0 Ω resistor to enable the bypass path.
►
Close Switch 2 (ON position) from Switch Array S1 (see
►
.
FB
to power down the now unused U2 amplifier.
Stage 2 Alternative Amplifiers
By default, Stage 2 houses an
differential amplifier. Note that it is possible to use alternative
amplifiers; however, these amplifiers are not included on the EVAL-
AD4080-FMCZ.
The ADA4940-1
sumption in this stage. When using the ADA4940-1, the noise
and distortion performance are expected to degrade relative to the
ADA4945-1.
The ADA4932-1
(2)
formance is critical or applications where distortion performance is
required up to 10 MHz. However, the improved distortion perform-
ance comes at the expense of higher power consumption.
Both the ADA4940-1 and ADA4932-1 are footprint compatible with
ADA4945-1, although some pin connections must be changed. The
necessary changes to use an alternative amplifier are as follows:
Remove ADA4945-1 from the U3 footprint.
►
Populate U3 with the ADA4940-1 or ADA4932-1.
►
For the JP3, JP4, JP5, JP6 solder links, remove the default
►
linkage (Pad 2 to Pad 3) and link Pad 1 to Pad 2 instead.
EVAL-AD4080
ADA4945-1 driving the ADC sets its output
ADA4945-1 low distortion, fully
can be used to achieve the lowest power con-
can be used for applications where distortion per-
AD4080
Table 3)
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