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SMP04EQ View Datasheet(PDF) - Analog Devices

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SMP04EQ Datasheet PDF : 15 Pages
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SMP04
Sample-Mode Distortion Characteristics
Although designed as a sample-and-hold, the SMP04 may be
used as a straight buffer amplifier by configuring it in a continu-
ous sample mode. This is done by connecting the S/H control
pin to a logic LOW. Its buffer bandwidth is primarily limited by
the distortion content as the signal frequency increases. Figure
17 shows the distortion characteristics of the SMP04 versus
frequency. It maintains less than 1% total harmonic distortion
over a voiceband of 8 kHz. Output spot noise voltage measures
4 nV/Hz at f = 1 kHz.
10
VS = ؎6V
VIN = 4Vp-p
1
different sampling frequencies of 14.4 kHz, 9.6 kHz and
7.2 kHz. The signal-to-noise ratios measure 58.2 dB, 59.3 dB
and 60 dB respectively.
Figure 19 depicts SMP04’s spectral response operating with
voice frequency of 3 kHz sampling at a 15.7 kHz rate. Under
this condition, the signal-to-noise measures 53 dB.
10 dB/DIV RANGE 15.0 dBm 5.9 dBm
0.1
0.010
0.001
0.0005
20
100
1k
10k
FREQUENCY – Hz
100k 200k
Figure 17. THD+N vs. Frequency
Sampled Data Dynamic Performance
In continuous sampled data applications such as voice digitiza-
tion or communication circuits, it is important to analyze the
spectral response of a sample-and-hold. Figures 16a and 16b
show the SMP04 sampling at a frequency of 86 kHz with a
1.4 V p-p pure sine wave input of 20 kHz and 8 kHz respec-
tively. The photos include the sampling carrier frequency as
well as its multiplying frequencies. In the case of the 20 kHz
carrier frequency, the second harmonic measures 41 dB down
from the fundamental, because the second is dominant, the
signal-to-noise ratio is –40.9 dB. The 8 kHz case produces an
improved S/N performance of –48 dB.
In the V.32 and V.33 modem environment, where a 1.8 kHz
carrier signal frequency is applied to the SMP04, Figure 18
compares the spectral responses of the SMP04 under three
START 1 000.0 Hz
STOP 20 000.0 Hz
Figure 19. SMP04 Spectral Response with an Input Carrier
Frequency of 3 kHz and the Sampling Frequency of 15.7 kHz
Sampled Data Dynamic Performance
In continuous sampled data applications such as voice digitiza-
tion or communication circuits, it is important to analyze the
spectral response of a sample-and-hold. Figures 16a and 16b
show the SMP04 sampling at a frequency of 86 kHz with a
1.4 V p-p pure sine wave input of 20 kHz and 8 kHz respec-
tively. The photos include the sampling carrier frequency as well
as its multiplying frequencies. In the case of the 20 kHz carrier
frequency, the second harmonic measures 41 dB down from the
fundamental, because the second is dominant, the signal-to-
noise ratio is –40.9 dB. The 8 kHz case produces an improved
S/N performance of –48 dB.
In the V.32 and V.33 modem environment, where a 1.8 kHz
carrier signal frequency is applied to the SMP04, Figure 18
compares the spectral responses of the SMP04 under three
different sampling frequencies of 14.4 kHz, 9.6 kHz and
7.2 kHz. The signal-to-noise ratios measure 58.2 dB, 59.3 dB
and 60 dB respectively.
10 dB/DIV RANGE 15.0 dBm 5.9 dBm
10 dB/DIV RANGE 15.0 dBm 5.7 dBm
10 dB/DIV RANGE 15.0 dBm 5.2 dBm
CENTER 10 500.0 Hz
SPAN 19 000.0 Hz
START 1 000.0 Hz
STOP 12 000.0 Hz
START 1 000.0 Hz
STOP 12 000.0 Hz
a.
b.
c.
Figure 18. SMP04 Spectral Response with a 1.8 kHz Carrier Frequency. (a) Shows the Sampling Frequency at 14.4 kHz;
it Exhibits a S/N Ratio of 58.2 dB. (b) Shows a 59.3 dB S/N at a Sampling Frequency of 8.6 kHz. (c) Shows a 60 dB S/N at
7.2 kHz.
REV. D
–9–
 

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