MAX108 Maxim, MAX108 Datasheet - Page 17

• Manufacturer Part Number: MAX108
• Description: 5V / 1.5Gsps / 8-Bit ADC with On-Chip 2.2GHz Track/Hold Amplifier
• Manufacturer: Maxim

Figure 9. Simplified Analog Input Structure (Single-Ended/
Differential)
In a typical single-ended configuration, the analog
input signal (Figure 10a) enters the T/H amplifier stage
at the in-phase input (VIN+), while the inverted phase
input (VIN-) is reverse-terminated to GNDI with an
external 50Ω resistor. Single-ended operation allows for
an input amplitude of ±250mV. Table 3 shows a selec-
tion of input voltages and their corresponding output
codes for single-ended operation.
To obtain a full-scale digital output with differential input
drive (Figure 10b), 250mVp-p must be applied between
VIN+ and VIN- (VIN+ = +125mV, and VIN- = -125mV).
Midscale digital output codes (01111111 or 10000000)
occur when there is no voltage difference between
VIN+ and VIN-. For a zero-scale digital output code, the
Table 3. Ideal Input Voltage and Output Code Results for Single-Ended Operation
ANALOG INPUTS ARE ESD PROTECTED
(NOT SHOWN IN THIS SIMPLIFIED DRAWING).
VIN+
GNDI
VIN-
+250mV - 1LSB
-250mV + 1LSB
+250mV
-250mV
VIN+
50
50
0V
______________________________________________________________________________________
Differential Analog Inputs
On-Chip 2.2GHz Track/Hold Amplifier
V
EE
VIN-
0V
0V
0V
0V
0V
±5V, 1.5Gsps, 8-Bit ADC with
+2.8V
OVERRANGE BIT
in-phase (VIN+) input must see -125mV and the invert-
ed input (VIN-) must see +125mV. A differential input
drive is recommended for best performance. Table 4
represents a selection of differential input voltages and
their corresponding output codes.
Figure 10a. Single-Ended Analog Input Signals
Figure 10b. Differential Analog Input Signals
INPUT RANGE
1
0
0
0
0
INPUT RANGE
FS ANALOG
FS ANALOG
500mVp-p
±250mV
+125mV
-125mV
+250mV
-250mV
250mV
500mV
V
IN
00000000 (zero scale)
11111111 (full scale)
= ±250mV
V
OUTPUT CODE
IN+
11111111
01111111
10000000
-250mV
0000001
toggles
V
IN+
V
IN-
V
IN-
0V
0V
t
t
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