AD9276-65EBZ Analog Devices Inc, AD9276-65EBZ Datasheet - Page 33

• Manufacturer Part Number: AD9276-65EBZ
• Description: 65MSPS ADC Converter Evaluation Board
• Manufacturer: Analog Devices Inc

Specifications of AD9276-65EBZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: ADC
• Kit Application Type: Data Converter
• Silicon Core Number: AD9276
• Number Of Adc's: 1
• Number Of Bits: 12
• Sampling Rate (per Second): 65M
• Data Interface: Serial, SPI™
• Inputs Per Adc: 1 Differential
• Input Range: *
• Power (typ) @ Conditions: 195mW @ 40MSPS
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9276
• Development Tool Type: Hardware - Eval/Demo Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADC
The AD9276 uses a pipelined ADC architecture. The quantized
output from each stage is combined into a 12-bit result in the
digital correction logic. The pipelined architecture permits the
first stage to operate on a new input sample and the remaining
stages to operate on preceding samples. Sampling occurs on the
rising edge of the clock.
The output staging block aligns the data, corrects errors, and
passes the data to the output buffers. The data is then serialized
and aligned to the frame and output clocks.
CLOCK INPUT CONSIDERATIONS
For optimum performance, the AD9276 sample clock inputs
(CLK+ and CLK−) should be clocked with a differential signal.
This signal is typically ac-coupled into the CLK+ and CLK− pins
via a transformer or capacitors. These pins are biased internally
and require no additional bias.
Figure 63 shows the preferred method for clocking the AD9276.
A low jitter clock source, such as the Valpey Fisher oscillator
VFAC3-BHL−50 MHz, is converted from single-ended to differ-
ential using an RF transformer. The back-to-back Schottky
diodes across the secondary transformer limit clock excursions
into the AD9276 to approximately 0.8 V p-p differential. This
helps to prevent the large voltage swings of the clock from
feeding through to other portions of the AD9276, and it
preserves the fast rise and fall times of the signal, which are
critical to low jitter performance.
If a low jitter clock is available, another option is to ac-couple
a differential PECL signal to the sample clock input pins, as
shown in Figure 64. The AD951x family of clock drivers offers
excellent jitter performance.
*
50Ω RESISTOR IS OPTIONAL.
VFAC3
VFAC3
3.3V
3.3V
OUT
OUT
50Ω
Figure 63. Transformer-Coupled Differential Clock
*
50Ω 100Ω
0.1µF
0.1µF
0.1µF
Figure 64. Differential PECL Sample Clock
CLK
CLK
ADT1-1WT, 1:1Z
MINI-CIRCUITS
PECL DRIVER
AD951x FAMILY
XFMR
0.1µF
240Ω
0.1µF
0.1µF
SCHOTTKY
HSM2812
DIODES:
240Ω
100Ω
0.1µF
0.1µF
CLK+
CLK–
CLK+
CLK–
ADC
ADC
Rev. 0 | Page 33 of 48
In some applications, it is acceptable to drive the sample clock
inputs with a single-ended CMOS signal. In such applications,
CLK+ should be driven directly from a CMOS gate, and the
CLK− pin should be bypassed to ground with a 0.1 μF capacitor
in parallel with a 39 kΩ resistor (see Figure 66). Although the
CLK+ input circuit supply is AVDD1 (1.8 V), this input is
designed to withstand input voltages of up to 3.3 V, making the
selection of the drive logic voltage very flexible.
Clock Duty Cycle Considerations
Typical high speed ADCs use both clock edges to generate a
variety of internal timing signals. As a result, these ADCs may
be sensitive to the clock duty cycle. Commonly, a 5% tolerance is
required on the clock duty cycle to maintain dynamic performance
characteristics. The AD9276 contains a duty cycle stabilizer (DCS)
that retimes the nonsampling edge, providing an internal clock
signal with a nominal 50% duty cycle. This allows a wide range
of clock input duty cycles without affecting the performance of
the AD9276. When the DCS is on, noise and distortion perfor-
mance are nearly flat for a wide range of duty cycles. However,
some applications may require the DCS function to be off. If so,
keep in mind that the dynamic range performance can be affected
when operated in this mode. See Table 18 for more details on
using this feature.
*
*
50Ω RESISTOR IS OPTIONAL.
50Ω RESISTOR IS OPTIONAL.
*
50Ω RESISTOR IS OPTIONAL.
VFAC3
VFAC3
3.3V
3.3V
VFAC3
OUT
OUT
3.3V
OUT
50Ω
Figure 66. Single-Ended 1.8 V CMOS Sample Clock
Figure 67. Single-Ended 3.3 V CMOS Sample Clock
0.1µF
0.1µF
*
50Ω
50Ω
Figure 65. Differential LVDS Sample Clock
0.1µF
0.1µF
0.1µF
0.1µF
*
*
CLK
CLK
LVDS DRIVER
CLK
CLK
CLK
CLK
CMOS DRIVER
CMOS DRIVER
AD951x FAMILY
AD951x FAMILY
AD951x FAMILY
0.1µF
OPTIONAL
OPTIONAL
100Ω
100Ω
100Ω
0.1µF
0.1µF
39kΩ
0.1µF
0.1µF
0.1µF
CLK+
CLK–
CLK+
CLK–
CLK+
CLK–
AD9276
ADC
ADC
ADC