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AD9058 View Datasheet(PDF) - Analog Devices

Part Name
Description
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AD9058
ADI
Analog Devices ADI
AD9058 Datasheet PDF : 11 Pages
1 2 3 4 5 6 7 8 9 10
AD9058
AD9058 in through-hole PCB designs, use the AD9058AJD/AKD
with individual pin sockets (AMP Part No. 6-330808-0). Alterna-
tively, surface-mount AD9058 units can be mounted in a
through-hole socket (Circuit Assembly Corporation, Irvine, Cali-
fornia Part No. CA-44SPC-T).
AD9058 APPLICATIONS
Combining two ADCs in a single package is an attractive alterna-
tive in a variety of systems when cost, reliability, and space are
important considerations. Different systems emphasize particular
specifications, depending on how the part is used.
In high density digital radio communications, a pair of high
speed ADCs are used to digitize the in-phase (I) and quadrature
(Q) components of a modulated signal. The signal presented to
each ADC in this type of system consists of message-dependent
amplitudes varying at the symbol rate, which is equal to the
sample rates of the converters.
ANALOG
INPUT
N
tA
N+1
N+2
ENCODE
tV
D0–D7 VALID DATA
FOR N–1
VALID DATA
FOR N
VALID DATA
FOR N+1
tPD
DATA
CHANGING
tA = APERTURE TIME
tV = DATA DELAY OF PRECEDING ENCODE
tPD = OUTPUT PROPAGATION DELAY
Figure 4. Timing Diagram
Figure 5 shows what the analog input to the AD9058 would
look like when observed relative to the sample clock. Signal-to-
noise ratio (SNR), transient response, and sample rate are all
critical specifications in digitizing this “eye pattern.”
ANALOG
INPUT
the time required for the AD9058 to achieve full accuracy when
a step function input is applied. Overvoltage recovery time is the
interval required for the AD9058 to recover to full accuracy after an
overdriven analog input signal is reduced to its input range.
Time domain performance of the ADC is also extremely important
in digital oscilloscopes. When a track-/sample-and-hold is used
ahead of the ADC, its operation becomes similar to that described
above for receivers.
The dynamic response to high frequency inputs can be described by
the effective number of bits (ENOB). The effective number of
bits is calculated with a sine wave curve fit and is expressed as:
[ ] ENOB = N LOG2 Error (measured) Error (ideal)
where N is the resolution (number of bits) and measured error is
actual rms error calculated from the converter’s outputs with
a pure sine wave applied as the input.
Maximum conversion rate is defined as the encode (sample)
rate at which SNR of the lowest frequency analog test signal
drops no more than 3 dB below the guaranteed limit.
60
55
+25 C
50
–55 C
+125 C
45
40
35
30
0.1
1
10
100
INPUT FREQUENCY – MHz
Figure 6. Harmonic Distortion vs. Analog Input Frequency
55
SAMPLE
CLOCK
Figure 5. I and Q Input Signals
Receiver sensitivity is limited by the SNR of the system. For the
ADC, SNR is measured in the frequency domain and calculated
with a Fast Fourier Transform (FFT). The signal-to-noise ratio
equals the ratio of the fundamental component of the signal
(rms amplitude) to the rms level of the noise. Noise is the sum
of all other spectral components, including harmonic distortion,
but excluding dc.
Although the signal being sampled does not have a significant
slew rate at the instant it is encoded, dynamic performance of
the ADC and the system is still critical. Transient response is
50
8.0
+25 C AND +125 C
45
7.2
40
6.4
–55 C
35
5.5
30
0.1
1
10
100
INPUT FREQUENCY – MHz
Figure 7. Dynamic Performance vs. Analog Input
Frequency
–8–
REV. E
 

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