VR2
Y1
VR1
T1
U4
Q5
Q2
L4
+5V
GND
+5V
-5.2V
P1
POWER CONNECTOR
L2
L3
L1
U6
Q4
Q3
TP3
AGND
TP3
AGND
NATIONAL SEMICONDUCTOR
ADC08100/ADC08200 EVAL BOARD
U8
U7
HP1
TP5
DGND
HP2
DL1
DL0
U5
U2
U3
Socket
TP1
PD
TP9
+3V
TP8
DGND
U1
Q1
TP4
VRB
J1
NUM_MEM
J4
CLK_SEL
J3
D4
INPUT
TP7
J2
INPUT
TP2
VRT
DIV_EN
J5
TP9
+3V
TP1
PD
J1
NUM_MEM
TP4
VRB
VR2
VRT ADJ
VR1
VRB ADJ
J2
INPUT BNC
TP2
VRT
TP7
INPUT
J4
CLK_SEL
J4
Detail:
Default Position
J5
Detail:
Default
is open
J1
Detail:
Hard-wired
Default Position
Figure 1. Component and Test Point Locations
4.0 Functional Description
4.2 ADC reference circuitry
The ADC08100 Evaluation Board schematic is shown in
Figure 2
.
The provided reference circuitry will provide nominal
reference voltage ranges of 1.3V to 2.6V for VRT and 0V
to 1.3V for VRB, Providing for nominal input ranges of 0V
to 2.6V peak-to-peak. Note that this is beyond the
maximum specified 2.3V range of the ADC08100.
4.1 Input (signal conditioning) circuitry
The input signal to be digitized should be applied to BNC
connector J2. This 50 Ohm input is intended to accept a
low-noise sine wave signal of 1.5V peak-to-peak
amplitude. To accurately evaluate the ADC08100
dynamic performance, the input test signal should be
passed through a high-quality bandpass filter (60dB
minimum stop-band attenuation) as even the best
generators do not provide a pure enough sine wave to
properly evaluate an ADC.
The reference voltages for the ADC08100 can be
monitored at test points TP2 and TP4 and are set with
VR1 and VR2. Signal offset can be provided by adjusting
both of these potentiometers, or by minor adjustments to
the +5 Volts at pin 1 of Power Connector P1.
4.3 ADC clock circuit
The clock signal applied to the ADC is selected with
jumper J4. A standard ECL-level 100 MHz crystal
oscillator should be installed at Y1 and the divide by 2
function selected by shorting pins 1 and 2 of jumper JP4.
Resistors R15, R15A, R16 and R18 provide the needed
input bias to the ADC08100. You can center the input
signal to the ADC by adjusting reference voltages VRT
and VRB with VR1 and VR2 or by making slight
adjustments to voltage an Power Connector pin 1.
6
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