AD1878 Просмотр технического описания (PDF) - Analog Devices

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AD1878

High Performance 16-/18-Bit ΣΔ Stereo ADCs

Analog Devices 

AD1878/AD1879

DEFINITIONS

Dynamic Range

The ratio of a full-scale output signal to the integrated output

noise in the passband (0 kHz to 20 kHz), expressed in decibels

(dB). Dynamic range is measured with a –60 dB input signal

and is equal to (S/[THD+N]) + 60 dB.

Signal to (Noise + Distortion)

The ratio of the root-mean-square (rms) value of the fundamen-

tal input signal to the rms sum of all spectral components in the

passband, expressed in decibels (dB).

Signal to Total Harmonic Distortion (THD)

The ratio of the rms sum of all harmonically related spectral

components in the passband to the fundamental input signal,

expressed either as a percentage (%) or in decibels (dB).

Passband

The region of the frequency spectrum unaffected by the attenu-

ation of the digital decimator’s filter.

Passband Ripple

The peak-to-peak variation in amplitude response from equal

amplitude input signal frequencies within the passband, ex-

pressed in decibels.

Stopband

The region of the frequency spectrum attenuated by the digi-

tal decimator’s filter to the degree specified by “stopband

attenuation.”

Gain Error

With a near full-scale input, the ratio of actual output to ex-

pected output, expressed as a percentage.

Interchannel Gain Mismatch

With near full-scale inputs, the ratio of outputs of the two stereo

channels, expressed in decibels.

Gain Drift

Change in response to a near full-scale input with a change in

temperature, expressed as parts-per-million (ppm) per °C.

Midscale Offset Error

Output response to a midscale input (i.e., zero volts dc), ex-

pressed in least-significant bits (LSBs).

Midscale Drift

Change in midscale offset error with a change in temperature,

expressed as parts-per-million (ppm) of full scale per °C.

Crosstalk

Ratio of response on one channel with a grounded input to a

full-scale 1 kHz sine-wave input on the other channel, expressed

in decibels.

Interchannel Phase Deviation

Difference in input sampling times between stereo channels, ex-

pressed as a phase difference in degrees between 1 kHz inputs.

Power Supply Rejection

With analog inputs grounded, energy at the output when a

300 mV p-p signal is applied to power supply pins, expressed in

decibels of full scale.

Group Delay

Intuitively, the time interval required for an input pulse to ap-

pear at the converter’s output, expressed in milliseconds (ms).

More precisely, the derivative of radian phase with respect to

radian frequency at a given frequency.

Group Delay Variation

The difference in group delays at different input frequencies.

Specified as the difference between largest and the smallest

group delays in the passband, expressed in microseconds (µs).

AD1878/AD1879 PIN LIST

Pin Input/Output Pin Name Description

11 I/O

12 I/O

13 I

14 I

15 I

16 I

17

18 I

19 I

10 I

11 I

12 I

13 I

14 I/O

15 I/O

16 I

17 I

18 I

19 I

20 I

21 I

22 I

23 I

24 I

25 I

26 I

27 O

28 I/O

LRCK

BCK

S0

64/32

DVDD

DGND

N/C

AVSS1

AVSS2

AGND

APD

VINR–

VINR+

REFR

REFL

VINL+

VINL–

AGND

AVDD1

AVDD2

AVSS1

DVDD

DGND

RESET

S1

CLOCK

DATA

WCK

Left/Right Clock

Bit Clock

Mode Select 0

Bit Rate Select

+5 V Digital Supply

Digital Ground

No Connection; Do Not Connect

–5 V Analog Supply

–5 V Analog Logic Supply

Analog Ground

Analog Power Down

Right Inverting Input

Right Noninverting Input

Right Reference Capacitor

Left Reference Capacitor

Left Noninverting Input

Left Inverting Input

Analog Ground

+5 V Analog Supply

+5 V Analog Logic Supply

–5 V Analog Supply

+5 V Digital Supply

Digital Ground

Reset

Mode Select 1

Master Clock Input

Serial Data Output

Word Clock

THEORY OF OPERATION

∑∆ Modulator Noise-Shaping

The stereo, differential analog modulators of the AD1878/

AD1879 employ a proprietary feedforward and feedback archi-

tecture that passes input signals in the audio band with a unity

transfer function yet simultaneously shape the quantization

noise generated by the one-bit comparator out of the audio

band. See Figure 1. Without the ∑∆ architecture, this quantiza-

tion noise would be spread uniformly from dc to one-half the

oversampling frequency, 64 × FS. (Regardless of architecture,

64 times oversampling by itself significantly reduces the quanti-

zation noise in the audio band if the input is properly dithered.

However, the noise reduction is only [log2 64] × 3 dB = 18 dB.)

PIN 1

2

8

1

0.250

(6.35)

MAX

0.200 (5.05)

0.125 (3.18)

0.022 (0.558)

0.014 (0.356)

15

14

0.580 (14.73)

0.485 (12.32)

1.565 (39.70)

1.380 (35.10)

0.060 (1.52)

0.015 (0.38)

0.100

(2.54)

BSC

0.625 (15.87)

0.600 (15.24)

0.015 (0.381)

0.008 (0.204)

0.070 (1.77)

MAX

0.150

(3.81)

MIN

SEATING

PLANE

0.195 (4.95)

0.125 (3.18)

Figure 1. AD1878/AD1879 Modulator Noise-Shaper (One

Channel)

REV. 0

–5–

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