AD1866 데이터 시트보기 (PDF) - Analog Devices

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AD1866

Single Supply Dual 16-Bit Audio DAC

Analog Devices 

VOR

+ 5V

+ 5V

VOL

VOL

FALSE GROUND

(2.5V)

+ 5V

VOR

Analog Circuit Considerations–AD1866

AD1866

1 VL

VBL 16

2 LL

VS 15

3 DL

VOL 14

4 CLK

NRL 13

5 DR

AGND 12

6 LR

NRR 11

7 DGND

8 VBR

VOR 10

VS 9

+5V

VOL

+5V

VOR

Figure 8a. Schematic Using False Ground

Figure 8a illustrates the traditional approach used to generate

false ground voltages in single supply audio systems. This cir-

cuit requires additional power and circuit board space.

The AD1866 eliminates the need for “false ground” circuitry.

VBR and VBL generate the required bias voltages previously

generated by the “false ground.” As shown in Figure 8b, VBR

and VBL may be used as the reference point in each output

channel. This permits a dc coupled output signal path. This

eliminates ac coupling capacitors and improves low frequency

performance. It should be noted that these bias outputs have

relatively high output impedance and will not drive output cur-

rents larger than 100 µA without degrading the specified

performance.

Figure 8b. Circuitry Using Voltage Biases

DISTORTION PERFORMANCE AND TESTING

The THD+N figure of an audio DAC represents the amount of

undesirable signal produced during reconstruction and play-

back of an audio waveform. Therefore, the THD+N specifica-

tion provides a direct measure to classify and choose an audio

DAC for a desired level of performance. Figure 1 illustrates the

typical THD+N versus frequency performance of the AD1866.

It is evident that the THD+N performance of the AD1866 re-

mains stable at all three amplitude levels through a wide range

of frequencies. A load impedance of at least 2 kΩ is recom-

mended for best THD+N performance.

Analog Devices tests all AD1866s on the basis of THD+N per-

formance. During the distortion test, a high speed digital pat-

tern generator transmits digital data to each channel of the

device under test. Sixteen-bit data is latched into the DAC at

352.8 kHz (8 × FS). The test input code is a digitally encoded

990.5 Hz sine wave with 0 dB, –20 dB, and –60 dB amplitudes.

A 4096 point FFT calculates total harmonic distortion + noise,

signal-to-noise ratio, and D-range. No deglitchers or external

adjustments are used.

REV. 0

–7–

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