AD9060JZ Analog Devices Inc, AD9060JZ Datasheet - Page 6

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AD9060JZ

Manufacturer Part Number
AD9060JZ
Description
IC ADC 10BIT 75MSPS 68-CLCC
Manufacturer
Analog Devices Inc
Datasheet

Specifications of AD9060JZ

Number Of Bits
10
Sampling Rate (per Second)
75M
Data Interface
Parallel
Number Of Converters
1
Power Dissipation (max)
3.5W
Voltage Supply Source
Dual ±
Operating Temperature
0°C ~ 70°C
Mounting Type
Surface Mount
Package / Case
68-CLCC

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AD9060
THEORY OF OPERATION
Refer to the Functional Block Diagram. As shown, the AD9060
uses a modified “flash,” or parallel, A/D architecture. The ana-
log input range is determined by an external voltage reference
(+V
ladder divides this reference into 512 steps, each representing
two quantization levels. Taps along the resistor ladder (1/4
1/2
formance is achieved by driving these points at 1/4, 1/2, and 3/4,
respectively, of the voltage reference range.
The A/D conversion for the nine most significant bits (MSB) is
performed by 512 comparators. The value of the least significant
bit (LSB) is determined by a unique interpolation scheme between
adjacent comparators. The decoding logic processes the com-
parator outputs and provides a 10-bit code to the output stage
of the converter.
Flash architecture has an advantage over other A/D architectures
because conversion occurs in one step. This means the perfor-
mance of the converter is limited primarily by the speed and
matching of the individual comparators. In the AD9060, an innova-
tive interpolation scheme takes advantage of the flash architecture
but minimizes the input capacitance, power, and device count
usually associated with that method of conversion.
These advantages occur because of using only half the normal
number of input comparator cells to accomplish the conversion.
In addition, a proprietary decoding scheme minimizes error codes.
Input control pins allow the user to select from among binary,
inverted binary, twos complement, and inverted twos complement
coding (see Table I, the AD9060 Truth Table).
APPLICATIONS
Many of the specifications used to describe A/D converters have
evolved from system performance requirements in these applica-
tions. Different systems emphasize particular specifications,
depending on how the part is used. The following applications
highlight some of the specifications and features that make the
AD9060 attractive in these systems.
Wideband Receivers
Radar and communication receivers (baseband and direct
IF digitization), ultrasound medical imaging, signal intelligence,
and spectral analysis all place stringent ac performance require-
ments on analog-to-digital converters (ADCs). Frequency domain
characterization of the AD9060 provides signal-to-noise ratio (SNR)
and harmonic distortion data to simplify selection of the ADC.
Receiver sensitivity is limited by the Signal-to-Noise Ratio (SNR)
of the system. The SNR for an ADC is measured in the frequency
domain and calculated with a Fast Fourier Transform (FFT).
The SNR equals the ratio of the fundamental component of the
signal (rms amplitude) to the rms value of the noise. The noise is
the sum of all other spectral components, including harmonic
distortion but excluding dc.
Good receiver design minimizes the level of spurious signals in
the system. Spurious signals developed in the ADC are the
result of imperfections in the device transfer function (non-
linearities, delay mismatch, varying input impedance, and
so on). In the ADC, these spurious signals appear as Harmonic
Distortion. Harmonic Distortion is also measured with an FFT
and is specified as the ratio of the fundamental component
of the signal (rms amplitude) to the rms value of the worst-
case harmonic (usually the second or third).
REF
REF
, and 3/4
and –V
REF
REF
) are provided to optimize linearity. Rated per-
), nominally ± 1.75 V. An internal resistor
REF
,
–6–
Two-Tone Intermodulation Distortion (IMD) is a frequently cited
specification in receiver design. In narrow-band receivers, third-
order IMD products result in spurious signals in the pass band
of the receiver. Like mixers and amplifiers, the ADC is charac-
terized with two, equal amplitude, pure input frequencies. The
IMD equals the ratio of the power of either of the two input
signals to the power of the strongest third order IMD signal.
Unlike mixers and amplifiers, the IMD does not always behave
as it does in linear devices (reduced input levels do not result in
predictable reductions in IMD).
Performance graphs provide typical harmonic and SNR data
for the AD9060 for increasing analog input frequencies. In
choosing an A/D converter, always look at the dynamic range
for the analog input frequency of interest. The AD9060 speci-
fications provide guaranteed minimum limits at three analog
test frequencies.
Aperture Delay is the delay between the rising edge of the ENCODE
command and the instant at which the analog input is sampled.
Many systems require simultaneous sampling of more than one
analog input signal with multiple ADCs. In these situations timing
is critical, and the absolute value of the aperture delay is not as
critical as the matching between devices.
Aperture Uncertainty, or jitter, is the sample-to-sample variation in
aperture delay. This is especially important when sampling high
slew rate signals in wide bandwidth systems. Aperture uncertainty
is one of the factors that degrades dynamic performance as the
analog input frequency is increased.
Digitizing Oscilloscopes
Oscilloscopes provide amplitude information about an observed
waveform with respect to time. Digitizing oscilloscopes must
accurately sample this signal without distorting the information
to be displayed.
One figure of merit for the ADC in these applications is Effective
Number of Bits (ENOB). ENOB is calculated with a sine wave
curve fit and equals
N is the resolution (number of bits) of the ADC. The measured
error is the actual rms error calculated from the converter outputs
with a pure sine wave input.
The Analog Bandwidth of the converter is the analog input fre-
quency at which the spectral power of the fundamental signal is
reduced 3 dB from its low frequency value. The analog bandwidth
is a good indicator of a converter’s slewing capabilities.
The Maximum Conversion Rate is defined as the encode rate
at which the SNR for the lowest analog signal test frequency
tested drops by no more than 3 dB below the guaranteed limit.
Imaging
Visible and infrared imaging systems each require similar char-
acteristics from ADCs. The signal input (from a CCD camera
or multiplexer) is a time division multiplexed signal consisting of
a series of pulses whose amplitude varies in direct proportion to
the intensity of the radiation detected at the sensor. These vary-
ing levels are then digitized by applying ENCODE commands at
the correct times, as shown in Figure 1.
ENOB
=
N
– log
2
[
Error measured Error ideal
(
)
(
REV. B
)
]

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