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dc1975fa
DEMO MANUAL DC1975A
ANALOG INPUT NETWORK
APPLYING POWER & SIGNALS TO THE DC1975 DEMONSTRATION
CIRCUIT
In the default setup both of the inputs are brought out to
SMA connectors so the demo board can be driven with
a differential source. The DC1975 is populated with no
filtering between the input SMAs and the ADC. There are
provisions for a custom filter to be designed and installed
between the off board driver and ADC.
A common-mode voltage is provided on turrets TP3 and
TP4 that can be used to bias the driver. If the driver is sup-
plying the common-mode voltage R10 and R20 should be
removed, and the common-mode voltage from the driver
can be connected on turrets TP3 and TP4.
In almost all cases, off-board filters will be required on the
analog inputs of the differential driver boards to achieve
data sheet SNR.
The off-board filters should be located close to the inputs
of the differential driver board to avoid reflections from
impedance discontinuities at the driven end of a long
transmission line. Most filters do not present 50Ω outside
the passband. In some cases, 3dB to 10dB pads may be
required to obtain low distortion.
Apply the analog input signal of interest to the SMA
connectors on the DC1975 demonstration circuit board
marked J1-J4.
If a DC890 is used to acquire data from the DC1975, the
DC890 must FIRST be connected to a powered USB port
or provided an external 6V to 9V BEFORE applying 4.5V to
6V across the pins marked V+ and GND on the DC1975.
DC1975 requires 4.5V for proper operation. Regulators
on the board produce the voltages required for the ADC.
The DC1975 demonstration circuit requires up to 300mA
depending on the sampling rate and the A/D converter
supplied.
The DC890 data collection board is powered by the USB
cable and does require an external power supply when
collecting data from an LVDS demo board. It must be
supplied an external 6V to 9V on turrets G7(+) and G1(–)
or the adjacent 2.1mm power jack.
