MAX109 Maxim Integrated Products, MAX109 Datasheet - Page 21

• Manufacturer Part Number: MAX109
• Description: 2.2Gsps ADC
• Manufacturer: Maxim Integrated Products

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Figure 9. Single-Ended Analog Input Signal Swing
Figure 10. Differential Analog Input Signal Swing
Figure 11. Offset Adjustment Circuit
Figure 12. Clock Input Structure
INPUT RANGE
SIMPLIFIED DIAGRAM
(INPUT ESD PROTECTION
NOT SHOWN).
INPUT RANGE
FS ANALOG
CLKCOM
500mV
FS ANALOG
CLKP
CLKN
±250mV
+125mV
POTENTIOMETER
-125mV
+250mV
-250mV
P-P
8-Bit, 2.2Gsps ADC with Track/Hold Amplifier
50Ω
50Ω
GNDI
10kΩ
______________________________________________________________________________________
REFOUT
250mV
500mV
V
IN
= ±250mV
VOSADJ
INP
and 1:4 Demultiplexed LVDS Outputs
INP
-250mV
GNDI
INN
INN
1V
0V
0V
V
EE
t
t
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.
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 50Ω 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
50Ω resistor. Single-ended operation allows for an input
amplitude of 500mV
input voltages and their corresponding output codes
for single-ended operation.
To obtain a full-scale digital output with differential input
drive (Figure 10), 250mV
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.
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
(R
with an external 10kΩ 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.
The MAX109 clock inputs are designed for either sin-
gle-ended or differential operation (Figure 12) with flexi-
VOSADJ
) of typically 50kΩ, VOSADJ can be driven
Applications Information
Single-Ended Analog Inputs
P-P
Differential Analog Inputs
. Table 4 shows a selection of
P-P
must be applied between
Clock Operation
Offset Adjust
21