datasheetbank_Logo   Integrated circuits, Transistor, Semiconductors Search and Datasheet PDF Download Site
Part Name :   

AD9060TE View Datasheet(PDF) - Analog Devices

Part NameDescriptionManufacturer
AD9060TE 10-Bit 75 MSPS A/D Converter ADI
Analog Devices ADI
AD9060TE Datasheet PDF : 12 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
AD9060
USING THE AD9060
Voltage References
The AD9060 requires the user to provide two voltage references:
+VREF and –VREF. These two voltages are applied across an inter-
nal resistor ladder (nominally 37 ) and set the analog input
voltage range of the converter. The voltage references should be
driven from a stable, low impedance source. In addition to these
two references, three evenly spaced taps on the resistor ladder
(1/4REF, 1/2REF, 3/4REF) are available. Providing a reference to
these quarter points on the resistor ladder will improve the inte-
gral linearity of the converter and improve ac performance. (AC
and dc specifications are tested while driving the quarter points
at the indicated levels.) The figure below is not intended to show
the transfer characteristic of the ADC but illustrates how the lin-
earity of the device is affected by reference voltages applied to
the ladder.
The select resistors (RS) shown in the schematic (each pair can
be a potentiometer) are chosen to adjust the quarter-point
voltage references but are not necessary if R1–R4 match
within 0.05%.
62
10.0
56
9.0
50
8.0
44
7.0
38
6.0
1111111111
(NOT TO SCALE)
TAPS
DRIVEN
1100000000
1000000000
TAPS
FLOATING
0100000000
IDEAL
LINEARITY
0000000000
–VSENSE
1/4REF
1/2REF
VIN
3/4REF +VSENSE
Effect of Reference Taps on Linearity
Resistance between the reference connections and the taps of the
first and last comparators causes offset errors. These errors,
called “top and bottom of the ladder offsets,” can be nulled by
using the voltage sense lines, +VSENSE and –VSENSE, to adjust the
reference voltages. Current through the sense lines should be
limited to less than 100 µA. Excessive current drawn through the
voltage sense lines will affect the accuracy of the sense line
voltage.
The next page shows a reference circuit that nulls out the offset
errors using two op amps, and provides appropriate voltage refer-
ences to the quarter-point taps. Feedback from the sense lines
causes the op amps to compensate for the offset errors. The two
transistors limit the amount of current drawn directly from the
op amps; resistors at the base connections stabilize their opera-
tion. The 10 kresistors (R1–R4) between the voltage sense
lines form an external resistor ladder; the quarter point voltages
are taken off this external ladder and buffered by an op amp. The
actual values of resistors R1–R4 are not critical, but they should
match well and be large enough (10 k) to limit the amount of
current drawn from the voltage sense lines.
32
5.0
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
±VSENSE – Volts
AD9060 SNR and ENOB vs. Reference Voltage
An alternative approach for defining the quarter-point references
of the resistor ladder to evaluate the integral linearity error of an
individual device and adjust the voltage at the quarter-points to
minimize this error. This may improve the low frequency ac
performance of the converter.
Performance of the AD9060 has been optimized with an analog
input voltage of ± 1.75 V (as measured at ± VSENSE). If the ana-
log input range is reduced below these values, relatively larger
differential nonlinearity errors may result because of comparator
mismatches. As shown in the figure below, performance of the
converter is a function of ± VSENSE.
Applying a voltage greater than 4 V across the internal resistor
ladder will cause current densities to exceed rated values and
may cause permanent damage to the AD9060. The design of
the reference circuit should limit the voltage available to the
references.
Analog Input Signal
The signal applied to ANALOG IN drives the inputs of 512
parallel comparator cells (see Equivalent Analog Input figure).
This connection has a typical input resistance of 7 kand input
capacitance of 45 pF. The input capacitance is nearly constant
over the analog input voltage range as shown in the graph, which
illustrates that characteristic.
The analog input signal should be driven from a low distortion,
low noise amplifier. A good choice is the AD9617, a wide band-
width, monolithic operational amplifier with excellent ac and dc
performance. The input capacitance should be isolated by a
small series resistor (24 for the AD9617) to improve the ac
performance of the amplifier (see AD9060/PCB Evaluation
Board Block Diagram).
–8–
REV. A
Direct download click here
 

Share Link : ADI
All Rights Reserved © datasheetbank.com 2014 - 2019 [ Privacy Policy ] [ Request Datasheet ] [ Contact Us ]