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AD9058JJ View Datasheet(PDF) - Analog Devices

Part Name
Description
View to exact match
AD9058JJ
ADI
Analog Devices ADI
AD9058JJ Datasheet PDF : 8 Pages
1 2 3 4 5 6 7 8
AD9058
ANALOG INPUT
N
tA
ENCODE
tV
D0 D 7
VALID DATA
FOR N 1
tPD
N+1
N+2
VALID DATA
FOR N
VALID DATA
FOR N + 1
t A = APERTURE TIME
tV = DATA DELAY OF
PRECEDING ENCODE
tPD = OUTPUT PROPAGATION DELAY
DATA
CHANGING
Figure 4. AD9058 Timing Diagram
Figure 5 below 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
SAMPLE
CLOCK
Figure 5. AD9058 I and Q Input Signals
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
+25°C
55
50
55°C
+125°C
45
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 the
time required for the AD9058 to achieve full accuracy when a
step function input is applied. Overvoltage recovery time is the in-
terval 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 impor-
tant 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
40
35
30
0.1
1
10
100
INPUT FREQUENCY MHz
Figure 6. Harmonic Distortion vs. Analog Input Frequency
55
+25°C AND +125°C
50
8.0
45
7.2
40
6.4
55°C
35
5.5
30
0.1
1
10
100
INPUT FREQUENCY MHz
Figure 7. AD9058 Dynamic Performance vs. Analog Input
Frequency
REV. B
–7–
 

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