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MAX109 Datasheet, PDF (21/29 Pages) Maxim Integrated Products – 8-Bit, 2.2Gsps ADC with Track/Hold Amplifier and 1:4 Demultiplexed LVDS Outputs | |||
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8-Bit, 2.2Gsps ADC with Track/Hold Amplifier
and 1:4 Demultiplexed LVDS Outputs
INP
+250mV
500mVP-P
FS ANALOG
INPUT RANGE
500mV
0V
INN
-250mV
t
VIN = ±250mV
Figure 9. Single-Ended Analog Input Signal Swing
+125mV
±250mV
FS ANALOG
INPUT RANGE
250mV
INP
-250mV
INN
0V
-125mV
t
Figure 10. Differential Analog Input Signal Swing
REFOUT
POTENTIOMETER
10kâ¦
GNDI
VOSADJ
Figure 11. Offset Adjustment Circuit
CLKP
50â¦
CLKCOM
50â¦
CLKN
1V
GNDI
SIMPLIFIED DIAGRAM
(INPUT ESD PROTECTION
NOT SHOWN).
VEE
Figure 12. Clock Input Structure
nal shift register is enabled and multiplexed with the
input of the 1:4 demultiplexer, replacing the quantizer
8-bit output. The test pattern consists of 8 bits. Table 3
depicts the composition of the first and last steps of the
PRN pattern. The entire look-up table can be down-
loaded from the Maxim website at www.maxim-ic.com.
Applications Information
Single-Ended Analog Inputs
The MAX109 is designed to work at full speed for both
single-ended and differential analog inputs; however,
for optimum dynamic performance it is recommended
that the inputs are driven differentially. Inputs INP and
INN feature on-chip, laser-trimmed 50⦠termination
resistors.
In a typical single-ended configuration, the analog
input signal (Figure 9) enters the T/H amplifier stage at
the in-phase input (INP), while the inverted phase input
(INN) is reverse-terminated to GNDI with an external
50⦠resistor. Single-ended operation allows for an input
amplitude of 500mVP-P. Table 4 shows a selection 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 10), 250mVP-P must be applied between
INP and INN (INP = 125mV and INN = -125mV). Mid-
scale digital output codes (01111111 or 10000000)
occur when there is no voltage difference between INP
and INN. For a zero-scale digital output code, the in-
phase INP input must see -125mV and the inverted
input INN must see 125mV. A differential input drive is
recommended for best performance. Table 5 repre-
sents a selection of differential input voltages and their
corresponding output codes.
Offset Adjust
The MAX109 provides a control input (VOSADJ) to
compensate for system offsets. The offset adjust input
is a self-biased voltage-divider from the internal 2.5V
precision reference. The nominal open-circuit voltage is
one-half the reference voltage. With an input resistance
(RVOSADJ) of typically 50kâ¦, VOSADJ can be driven
with an external 10k⦠potentiometer (Figure 11) con-
nected between REFOUT and GNDI to correct for offset
errors. For stabilizing purposes, decouple this output
with a 0.01µF capacitor to GNDI. VOSADJ allows for a
typical offset adjustment of ±10 LSB.
Clock Operation
The MAX109 clock inputs are designed for either sin-
gle-ended or differential operation (Figure 12) with flexi-
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