AD13280/PCB Analog Devices Inc, AD13280/PCB Datasheet - Page 14

• Manufacturer Part Number: AD13280/PCB
• Description: KIT EVAL PCB FOR AD13280
• Manufacturer: Analog Devices Inc

Specifications of AD13280/PCB

• Rohs Status: RoHS non-compliant
• Number Of Adc's: 2
• Number Of Bits: 12
• Sampling Rate (per Second): 80M
• Data Interface: Parallel
• Inputs Per Adc: 1 Differential
• Input Range: ±1 V
• Power (typ) @ Conditions: 3.7W @ 80MSPS
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -25°C ~ 85°C
• Utilized Ic / Part: AD13280

AD13280
THEORY OF OPERATION
The AD13280 is a high dynamic range 12-bit, 80 MHz pipeline
delay (three pipelines) analog-to-digital converter (ADC). The
custom analog input section provides input ranges of 1 V p-p
and 2 V p-p and input impedance configurations of 50 Ω, 100 Ω,
and 200 Ω.
The AD13280 employs four monolithic Analog Devices com-
ponents per channel (AD8045, AD8138, AD8031, and a custom
ADC IC), along with multiple passive resistor networks and
decoupling capacitors to fully integrate a complete 12-bit
analog-to-digital converter (ADC).
In the single-ended input configuration, the input signal is passed
through a precision laser-trimmed resistor divider, allowing the
user to externally select operation with a full-scale signal of ±0.5 V
or ±1.0 V by choosing the proper input terminal for the applica-
tion. The result of the resistor divider is to apply a full-scale
input of approximately 0.4 V to the noninverting input of the
internal AD8045 amplifier.
The AD13280 analog input includes an AD8045 amplifier
featuring an innovative architecture that maximizes the dynamic
range capability on the amplifier inputs and outputs. The AD8045
amplifier provides a high input impedance and gain for driving the
AD8138 in a single-ended to differential amplifier configuration.
The AD8138 has a −3 dB bandwidth at 300 MHz and delivers a
differential signal with the lowest harmonic distortion available in
a differential amplifier. The AD8138 differential outputs help
balance the differential inputs to the custom ADC, maximizing
the performance of the device.
The AD8031 provides the buffer for the internal reference
analog-to-digital converter. The internal reference voltage of
the custom ADC is designed to track the offsets and drifts and
is used to ensure matching over an extended temperature range
of operation. The reference voltage is connected to the output
common-mode input on the AD8138. This reference voltage
sets the output common mode on the AD8138 at 2.4 V, which
is the midsupply level for the ADC.
The custom ADC has complementary analog input pins, AIN
and AIN. Each analog input is centered at 2.4 V and should
swing ±0.55 V around this reference. Because AIN and AIN are
180 degrees out of phase, the differential analog input signal is
2.2 V peak-to-peak. Both analog inputs are buffered prior to
the first track-and-hold.
The custom ADC digital outputs drive 100 Ω series resistors
(see Figure 16). The result is a 12-bit, parallel digital CMOS-
compatible word, coded as a twos complement.
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USING THE SINGLE-ENDED INPUT
The AD13280 has been designed with user ease of operation in
mind. Multiple input configurations have been included on-
board to allow the user a choice of input signal levels and input
impedance. The standard inputs are ±0.5 V and ±1.0 V. The
user can select the input impedance of the AD13280 on any
input by using the other inputs as alternate locations for the
GND. The following is a summary of the impedance options
available at each input location:
AMP-IN-x-1 = 100 Ω when AMP-IN-x-2 is open.
AMP-IN-x-1 = 50 Ω when AMP-IN-x-2 is shorted to GND.
AMP-IN-x-2 = 200 Ω when AMP-IN-x-1 is open.
Each channel has two analog inputs: AMP-IN-A-1 and
AMP-IN-A-2 or AMP-IN-B-1 and AMP-IN-B-2. Use
AMP-IN-A-1 or AMP-IN-B-1 when an input of ±0.5 V full
scale is desired. Use AMP-IN-A-2 or AMP-IN-B-2 when ±1 V
full scale is desired. Each channel has an AMP-OUT that must
be tied to either a noninverting or inverting input of a
differential amplifier with the remaining input grounded. For
example, Side A, AMP-OUT-A (Pin 6) must be tied to A+IN
(Pin 5) with A−IN (Pin 4) tied to ground for noninverting
operation or AMP-OUT-A (Pin 6) tied to A−IN (Pin 4) with
A+IN (Pin 5) tied to ground for inverting operation.
USING THE DIFFERENTIAL INPUT
Each channel of the AD13280 is designed with two optional
differential inputs, A+IN, A−IN and B+IN, B−IN. The inputs
provide system designers with the ability to bypass the AD8045
amplifier and drive the AD8138 directly. The AD8138 differen-
tial ADC driver can be deployed in either a single-ended or
differential input configuration. The differential analog inputs
have a nominal input impedance of 620 Ω and nominal full-
scale input range of 1.2 V p-p. The AD8138 amplifier drives a
differential filter and the custom analog-to-digital converter.
The differential input configuration provides the lowest even-
order harmonics and signal-to-noise (SNR) performance
improvement of up to 3 dB (SNR = 73 dBFS). Exceptional care
was taken in the layout of the differential input signal paths.
The differential input transmission line characteristics are
matched and balanced. Equal attention to system level signal
paths must be provided in order to realize significant perform-
ance improvements.