Rainbow Electronics MAX104 - Manual (Page 17)

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 50
Ω
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.
Differential Analog Inputs
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
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.
MAX104
±5V, 1Gsps, 8-Bit ADC with
On-Chip 2.2GHz Track/Hold Amplifier
______________________________________________________________________________________ 17
+2.8V
50 Ω
50 Ω
VIN+
ANALOG INPUTS ARE ESD PROTECTED
(NOT SHOWN IN THIS SIMPLIFIED DRAWING).
VIN-
GNDI
V EE
Figure 9. Simplified Analog Input Structure (Single-Ended/
Differential)
V IN+
V
IN-
OV
+250mV
-250mV t
500mVp-p
FS ANALOG
INPUT RANGE
V IN = ±250mV
500mV
Figure 10a. Single-Ended Analog Input Signals
V
IN+
V
IN- +125mV
-125mV t
±250mV
FS ANALOG
INPUT RANGE
OV
250mV -250mV
Figure 10b. Differential Analog Input Signals
Table 3. Ideal Input Voltage and Output Code Results for Single-Ended Operation
0V 11111111 (full scale) +250mV
VIN-
1
OVERRANGE BIT VIN+ OUTPUT CODE
0V 11111111 +250mV - 1LSB 0
0V
0V
01111111
toggles
10000000
0V 0
0000001 -250mV + 1LSB 0
0V 00000000 (zero scale) -250mV 0