AD9212 Analog Devices, AD9212 Datasheet - Page 20

• Manufacturer Part Number: AD9212
• Description: Octal, 10-Bit, 40 MSPS/65 MSPS, Serial LVDS, 1.8 V ADC
• Manufacturer: Analog Devices

Specifications of AD9212

• Resolution (bits): 10bit
• # Chan: 8
• Sample Rate: 65MSPS
• Interface: LVDS,Ser
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p,2 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

AD9212
THEORY OF OPERATION
The AD9212 architecture consists of a pipelined ADC divided
into three sections: a 4-bit first stage followed by eight 1.5-bit
stages and a 3-bit flash. Each stage provides sufficient overlap
to correct for flash errors in the preceding stage. The quantized
outputs from each stage are combined into a final 10-bit result
in the digital correction logic. The pipelined architecture permits
the first stage to operate with a new input sample while the
remaining stages operate with preceding samples. Sampling
occurs on the rising edge of the clock.
Each stage of the pipeline, excluding the last, consists of a low
resolution flash ADC connected to a switched-capacitor DAC
and an interstage residue amplifier (for example, a multiplying
digital-to-analog converter (MDAC)). The residue amplifier
magnifies the difference between the reconstructed DAC output
and the flash input for the next stage in the pipeline. One bit of
redundancy is used in each stage to facilitate digital correction
of flash errors. The last stage simply consists of a flash ADC.
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 data clocks.
ANALOG INPUT CONSIDERATIONS
The analog input to the AD9212 is a differential switched-
capacitor circuit designed for processing differential input signals.
This circuit can support a wide common-mode range while
maintaining excellent performance. An input common-mode
voltage of midsupply minimizes signal-dependent errors and
provides optimum performance.
VIN + x
VIN – x
Figure 42. Switched-Capacitor Input Circuit
C
C
PAR
PAR
H
H
S
S
C
C
SAMPLE
SAMPLE
S
S
H
H
Rev. E | Page 20 of 56
The clock signal alternately switches the input circuit between
sample mode and hold mode (see Figure 42). When the input
circuit is switched into sample mode, the signal source must be
capable of charging the sample capacitors and settling within
one-half of a clock cycle. A small resistor in series with each
input can help reduce the peak transient current injected from
the output stage of the driving source. In addition, low-Q inductors
or ferrite beads can be placed on each leg of the input to reduce
high differential capacitance at the analog inputs and therefore
achieve the maximum bandwidth of the ADC. Such use of low-
Q inductors or ferrite beads is required when driving the converter
front end at high IF frequencies. Either a shunt capacitor or two
single-ended capacitors can be placed on the inputs to provide a
matching passive network. This ultimately creates a low-pass
filter at the input to limit unwanted broadband noise. See the
AN-742 Application
Switched-Capacitor ADCs; the
Resonant Approach to Interfacing Amplifiers to Switched-Capacitor
ADCs; and the Analog Dialogue article
Front-End for Wideband A/D
for more information. In general, the precise values depend on
the application.
The analog inputs of the AD9212 are not internally dc-biased.
Therefore, in ac-coupled applications, the user must provide
this bias externally. Setting the device so that V
recommended for optimum performance, but the device can
function over a wider range with reasonable performance, as
shown in Figure 45 and Figure 46.
Note, Frequency Domain Response of
Converters” (Volume 39, April 2005)
AN-827 Application
“Transformer-Coupled
Data Sheet
CM
= AVDD/2 is
Note, A