AD1862N-J Analog Devices, AD1862N-J Datasheet - Page 7

• Manufacturer Part Number: AD1862N-J
• Description: Ultralow Noise 20-Bit Audio DAC
• Manufacturer: Analog Devices

REV. A
TOTAL HARMONIC DISTORTION + NOISE
The THD figure of an audio DAC represents the amount of un-
desirable signal produced during reconstruction and playback of
an audio waveform. The THD specification, therefore, provides
a direct method to classify and choose an audio DAC for a de-
sired level of performance.
By combining noise measurement with the THD measurement,
a THD+N specification is realized. This specification indicates
all of the undesirable signal produced by the DAC, including
harmonic products of the test tone as well as noise.
Analog Devices tests all AD1862s on the basis of THD+N per-
formance. In this test procedure, a digital data stream represent-
ing a 0 dB, –20 dB or –60 dB sine wave is sent to the device
under test. The frequency of the waveform is 990.5 Hz. Input
data is sent to the AD1862 at an 8 F
AD1862 under test produces an output current which is con-
verted to an output voltage by an external amplifier. Figure 10
illustrates the recommended test circuit. Deglitchers and trims
are not used during this test procedure. The automatic test
equipment digitizes 4096 samples of the output test waveform,
incorporating 23 complete cycles of the sine wave. A 4096 point
FFT is performed on the test data.
352.8kHz
17MHz
S
rate (352.8 kHz). The
–
–
12V
12V
12V
0.1 F
Figure 10. Recommended Test Circuit
0.1 F
0.1 F
1
2
3
4
5
6
7
8
(Not to Scale)
AD1862
TOP VIEW
–7–
16
15
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13
12
11
10
9
Based upon the harmonics of the fundamental 990.5 Hz test
tone, and the noise components in the audio band, the total har-
monic distortion + noise of the device is calculated. The
AD1862 is available in two performance grades. The AD1862N
produces a maximum of 0.0025% THD+N at 0 dB signal lev-
els. The higher performance AD1862N-J produces a maximum
of 0.0016% THD+N at 0 dB signal levels.
SIGNAL-TO-NOISE RATIO
The Signal-to-Noise Ratio (SNR) of the AD1862 is tested in the
following manner. The amplitude of a 0 dB signal is measured.
The device under test is then set to midscale output voltage (0
volts). The amplitude of all noise present to 30 kHz is mea-
sured. The SNR is the ratio of these two measurements. The
SNR figure for the AD1862 includes the output noise contrib-
uted by the NE5534 op amp used in the test fixture but does
not include the noise contributed by the low-pass filter used in
the test fixture.
The AD1862N has a minimum SNR of 110 dB. The higher
performance AD1862N-J has a minimum SNR of 113 dB.
12V
10 F
+
0.1 F
360pF
DIGITAL
COMMON
Figure 9. External Amplifier Connections
+
1 F
SE5534A
1
2
3
4
5
6
8
7
(Not to Scale)
TOP VIEW
AD1862
LOW PASS
3-POLE
FILTER
Testing the AD1862
ANALOG
COMMON
16
15
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13
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10
9
OUTPUT
VOLTAGE
V
OUT