Data Sheet
AD1856
ANALOG CIRCUIT CONSIDERATIONS
+5V
16
GROUNDING RECOMMENDATIONS
+V
+V
S
L
The AD1856 has two ground pins, designated analog and digital
ground (AGND and DGND). The analog ground pin is the high
quality ground reference point for the analog portion of the
device. The digital ground pin returns ground current from the
digital logic portions of the AD1856 circuitry. Both pins should
be connected directly to a single solid ground plane, and the
components should be placed around the AD1856 so that analog
and digital return currents do not cross each other. A single solid
ground plane with good parts placement and trace routing yields
the quietest design with the best signal integrity and EMI/EMC
specifications.
3
AD1856
2
8
1
12
DGND
–V
–V
AGND
L
S
GROUND
–5V
Figure 3. Alternate Recommended Schematic
Given that these two supplies are within the range of 5 V to
12 V, they can be used to power the AD1856. In this case, the
positive logic and positive analog supplies can both be connected
to the single positive supply. The negative logic and negative analog
supplies can both be connected to the single negative supply.
Performance benefits from a measure of isolation between the
supplies, introduced by using simple low-pass filters in the
individual power supply leads.
POWER SUPPLIES AND DECOUPLING
The AD1856 has four power supply input pins. +VS and −VS
provide the supply voltages to operate the linear portions of the
DAC, including the voltage reference, output amplifier, and
control amplifier. The +VS and −VS supplies are designed to
operate from 5 V to 12 V.
As with most linear circuits, changes in the power supplies affect
the output of the DAC. Analog Devices recommends that well-
regulated power supplies with less than 1% ripple be incorporated
into the design of any system using these devices.
The +VL and −VL pins supply power to the digital portions of
the chip, including the input shift register and the input latching
circuitry. The +VL and −VL supplies are also designed to operate
from 5 V to 12 V, subject only to the limitation that +VL cannot
be more positive than +VS, and −VL cannot be more negative
than −VS.
TOTAL HARMONIC DISTORTION
The THD figure of an audio DAC represents the amount of
undesirable signal produced during reconstruction and play-
back of an audio waveform. The THD specification, therefore,
provides a direct method for classifying and choosing an audio
DAC for a desired level of performance.
Decoupling capacitors should be used on all power supply pins.
Furthermore, good engineering practice suggests that these
capacitors be placed as close as possible to the package pins. The
decoupling for both the bipolar logic supply, VL, and the bipolar
analog supply, VS, should be returned to the closest ground pins.
Analog Devices tests and grades all AD1856 devices on the
basis of THD performance. A block diagram of the test setup
is shown in Figure 4. In this test setup, a digital data stream,
representing a 0 dB, −20 dB, or −60 dB sine wave, is sent to the
device under test. The frequency of this waveform is 990.5 Hz.
Input data is sent to the AD1856 at a 4× fS rate (176.4 kHz). The
AD1856 under test produces an analog output signal with the
on-board op amp.
The use of four separate power supplies reduces feedthrough
from the digital portion of the system to the linear portions of
the system, thus contributing to good performance. However,
four separate voltage supplies are not necessary for good circuit
performance. For example, Figure 3 illustrates a system where
only a single positive and a single negative supply are available.
23 CYCLES
4× fS
DATA
AD1856
RATE
±3V
16-BIT
DATA
DIGITAL
WAVEFORM
GENERATOR
V
OUT
LE
CLK
990.5Hz
NOTCH
FILTER
30kHz
LOW-PASS
FILTER
0
1
1
0
1
0
1
0
1
1
0
OUTPUT
1
1
.
1
.
0
.
1
.
0
.
1
.
4096 PT.
FFT
ANALYZER
DIGITIZER
.
.
.
.
.
.
.
.
.
.
.
.
1
1
0
1
0
0
0
1
1
0
0
1
1
1
1
0
1
0
4096
SAMPLES
Figure 4. Block Diagram of Distortion Test Circuit
Rev. C | Page 9 of 16
5秒后页面跳转
资料手册解读：UC3842参数和管脚说明
一文带你了解无源晶振的负载电容为何要加两颗谐振电容CL1和CL2
玻璃管保险丝与陶瓷管保险丝：区别与替代性探讨
PCF8574资料解读：主要参数分析、引脚说明
微信公众号
抖音公众号
浙公网安备 33010502006866号 浙ICP备10014259号-119
营业执照ICP证
技术参数
数据手册
如果您发现信息不准确，
