ad1859jrz Analog Devices, Inc., ad1859jrz Datasheet - Page 8

• Manufacturer Part Number: ad1859jrz
• Description: Stereo, Single-supply 18-bit Integrated Dac
• Manufacturer: Analog Devices, Inc.

AD1859
Option for Analog De-emphasis Processing
The AD1859 includes three pins for implementing an external
analog 50/15 s (or possibly the CCITT J. 17) de-emphasis fre-
quency response characteristic. A control pin DEEMP (Pin 2)
enables de-emphasis when it is asserted HI. Two analog out-
puts, EMPL (Pin 3) and EMPR (Pin 26) are used to switch the
required analog components into the output stage of the AD1859.
An analog implementation of de-emphasis is superior to a digital
implementation in several ways. It is generally lower noise, since
digital de-emphasis is usually created using recursive IIR filters,
which inject limit cycle noise. Also the digital de-emphasis is be-
ing applied in front of the primary analog noise generation source,
the DAC modulator, and its high frequency noise contributions
are not attenuated. An analog de-emphasis circuit is down-
stream from the relatively “noisy” DAC modulator and thus pro-
vides a more effective noise reduction role (which was the original
intent of the emphasis/de-emphasis scheme). A final key advan-
tage of analog de-emphasis is that it is sample rate invariant, so
that users can fully exploit the sample rate range of the AD1859
and simultaneously use de-emphasis. Digital implementations gen-
erally only support fixed, standard sample rates.
Digital Phase Locked Loop
The digital PLL is adaptive, and locks to the applied sample rate
(on the LRCLK Pin 13) in 100 ms to 200 ms. The digital PLL
is initially in “fast” mode, with a wide lock capture bandwidth.
OPERATING FEATURES
Serial Data Input Port
The AD1859 uses the frequency of the left/right input clock to
determine the input sample rate. LRCLK must run continu-
ously and transition twice per stereo sample period (except in
the left-justified DSP serial port style mode, when it transitions
four times per stereo sample period). The bit clock (BCLK) is
edge sensitive and may be used in a gated or burst mode (i.e., a
stream of pulses during data transmission followed by periods of
inactivity). The bit clock is only used to write the audio data
into the serial input port. It is important that the left/right clock
is “clean” with monotonic rising and falling edge transitions and
no excessive overshoot or undershoot which could cause false
clock triggering of the AD1859.
The AD1859’s flexible serial data input port accepts data in
twos-complement, MSB-first format. The left channel data
field always precedes the right channel data field. The input
data consists of either 16 or 18 bits, as established by the 18/16
input control (Pin 8). All digital inputs are specified to TTL
logic levels. The input data port is configured by control pins.
LRCLK
SDATA
INPUT
INPUT
INPUT
BCLK
LSB
MSB
LEFT CHANNEL
MSB-1
MSB-2
Figure 2. Right-Justified Mode
LSB+2
LSB+1
LSB
–8–
Serial Input Port Modes
The AD1859 uses two multiplexed input pins to control the
mode configuration of the input data port. IDPM0 and IDPM1
program the input data port mode as follows:
Figure 2 shows the right-justified mode. LRCLK is HI for the
left channel, and LO for the right channel. Data is valid on the
rising edge of BCLK. The MSB is delayed 14-bit clock periods
(in 18-bit input mode) or 16-bit clock periods (in 16-bit input
mode) from an LRCLK transition, so that when there are 64
BCLK periods per LRCLK period, the LSB of the data will be
right-justified to the next LRCLK transition.
The phase detector automatically switches the loop filter into
“slow” mode as phase lock is gradually obtained. The loop
bandwidth is 15 Hz in slow mode. Since the loop filter is first
order, the digital PLL will reject jitter on the left/right clock
above 15 Hz, with an attenuation of 6 dB per octave. The jitter
rejection frequency response is shown in Figure 1.
IDPM1
LO
LO
HI
HI
–12
–18
–24
–30
–36
–42
–48
–54
–60
–6
0
Figure 1. Digital PLL Jitter Rejection
0
IDPM0
LO
HI
LO
HI
15
Hz ABOVE OR BELOW THE SAMPLE FREQUENCY
RIGHT CHANNEL
30
MSB
60
MSB-1
120
Serial Input Port Mode
Right-Justified (See Figure 2)
Left-Justified (See Figure 4)
Left-Justified DSP Serial Port Style
I
(See Figure 5)
MSB-2
2
S-Justified (See Figure 3)
240
480
960
LSB+2
1920
3840
LSB+1
7680
LSB
15360
REV. A