【写在前面：看到EE上有很多不错的文章，但是很多人阅读这样的文章有障碍，现在把这些精彩的文章贴出来，请大家用集体的智慧为彼此扫除障碍。来吧，请将你的译文贴在回复中。翻译一句不算少，翻译整篇不算多。
说明：
1、你看到红颜色的字体是已经被别人翻译过了的，所以你就不要再翻译了。
2、只要你翻译一段（最少一句话），你将获得6个积分。
3、解释一个词汇奖励5个积分。
4、楼主会在可能的情景下设问，能够正确回答问题的人将会获得由与非网提供的卓越购物卡。在回答正确的前提下，我们只奖励回答最早的。
设问：
[1] 在39楼的设问：请问这330MHz的带宽和200MHz的带宽是怎样计算出来的？
[2] 在47楼设问：如果谁能说出十种以上的示波器触发方式，与非网将奖励20元卓越购物卡一张。
[3]在53楼设问：请解释下“10-MW”的含义！
*正确，及时回答以上问题中的任意一个将会获得价值20元的卓越购物卡。回答该问题请到39楼，如果你知道答案直接跟贴即可。
*黑颜色的问题表示该问题尚未有人给出正确答案，回答后即可获奖。红颜色的问题表示已经有人给出了正确答案，你可以发表自己的见解，但是不会获得奖品。
】
Mixed-signal oscilloscopes (MSOs) solve a basic conundrum: Logic
analyzers have a large number of inputs but offer no analog
capabilities and typically are hard to use. In contrast,
oscilloscope operation is intuitive, but scopes have no more than
four channels. MSOs provide both analog and digital channels in a
familiar scope format.
The MSO name was coined by Agilent Technologies, at the time part
of Hewlett-Packard, when the MSO was introduced 10 years ago. This
instrument integrated either two or four conventional scope
channels with 16 logic-timing channels. Fortunately for today’s
engineers and technicians, the MSO terminology has caught on.
For example, LeCroy offers the MS Series MSO option for the
company’s WaveSurfer Xs and WaveRunner Xi product lines. Yokogawa
doesn’t use special designations but simply refers to the Model
DL9710L as a mixed-signal scope. Tektronix has adopted the MSO
prefix as part of the model number. Just as the company has a TDS
and a DPO series, now there is an MSO4000 Series as well.
Other than similar terminology, what common set of features can a
user expect to find across all brands of MSOs? There is remarkable
similarity among products from the four major scope manufacturers,
such as the wealth of display detail shown in Figure 1, but there
are important differences as well.
 Figure 1. Mixed-Signal Display With Digital and Analog Channels,
Serial Bus Decode, and Collapsed Bus
Courtesy of LeCroy |
Striking a Balance
Vendors agree that an MSO is not a logic analyzer. For example,
Chris Loberg, senior marketing manager at Tektronix, said, "Today’s
logic analyzers can acquire more than 100 channels to address
unique design challenges but may require hours to set up. In the
case of an MSO, it’s important to recognize that for most engineers
it is an instrument quickly deployed for important, yet simpler,
design verification tasks."
Clearly, 100 channels are too many, but how many digital channels
do you really need? Agilent continues to provide 16, the same
number as in the first MSO. Tektronix offers 16 and LeCroy 18
although LeCroy’s MS-500-36 option is a 36-channel version.
Yokogawa has opted for 32 channels as standard.
Digital channels can be grouped as buses for display and
triggering. A handy feature is the capability to include a given
channel in more than one group. This allows you to compare timing
of a number of channels to a common signal.
Viewing several related channels as a collapsed bus greatly
simplifies the display of many simultaneous traces without losing
information. Yokogawa provides a useful computed DAC function on a
group of digital channels, producing a multilevel waveform
representative of the successive digital bus values. Tektronix
offers multichannel setup and hold verification across a parallel
bus.
Serial bus decoding and triggering are important capabilities first
made available in the DSOs on which MSOs are based. One or more
scope analog channels can be used for this purpose on both the base
DSOs and derived MSOs from all four manufacturers. Buses dealt with
include I2C, CAN, SPI, UART, RS-232, FlexRay, and LIN. Not all
types of buses are available from all vendors, and bundling of bus
types within a single option varies by vendor.
LeCroy’s MS Series MSOs also can perform all the serial bus
decoding and trigger functions from digital channels, as can
Agilent MSOs. Yokogawa soon will have that capability for I2C and
SPI buses. Tektronix doesn’t distinguish between MSO and DSO
operation on this point.
Triggering across 20 or more channels is supported as are a number
of state and pattern triggers. According to Agilent’s Infiniium
8000 Series datasheet, for example, "There are no limitations on
the combination of analog and digital channels that can be used for
a particular pattern or state trigger setting."
However, a common feature of all four manufacturers’ datasheets is
a lack of details regarding the interaction between the digital and
analog channels. Clear statements, such as Agilent’s, help define
what you can and can’t assume.
Operation
While all MSOs provide valuable information about the timing
relationships among digital and analog channels, there are a few
operational limitations that you need to consider. MSOs are scopes
with additional digital channels added: How completely the extra
channels have been integrated makes all the difference.
Ideally, an MSO would offer at least 20 channels that performed as
uniformly as possible. Analog channels require a sensitive
preamplifier with a high input impedance and a fast,
high-resolution ADC. Digital channels must have sufficient
bandwidth and a fast comparator. The goal is to create an
architecture in which the data signals existing after the ADCs and
comparators are treated equally. The only difference should be the
1-bit resolution of the digital inputs vs. the n-bit resolution of
the analog channels.
In today’s MSOs, digital inputs and analog inputs have different
characteristics. The maximum allowable voltage ranges from ±15 V
for Tektronix to Agilent’s ±40-V peak CAT 1. The CAT 1
qualification implies a transient overvoltage capability not
included in Yokogawa’s unqualified ±40-V rating. LeCroy’s MS-500
has a maximum ±30-V rating.
Input impedance also typically is not the same as an analog
channel’s 1 MΩ. Tektronix specifies 20 kΩ, Agilent 100 kΩ//8 pF,
and LeCroy 100 kΩ//5 pF. Yokogawa offers the 100-MHz bandwidth type
701980 pod with 1-MΩ//10-pF impedance. The 250-MHz type 701981 pod
is specified with 10 kΩ//9 pF.
Bandwidth varies as well. Agilent and Tektronix specify the minimum
width pulse that can be acquired: 1.5 ns for Tektronix and 2.5 ns
for the Agilent Infiniium 8000 Series. These widths correspond
approximately to 330-MHz and 200-MHz bandwidths, respectively.
LeCroy offers three MS Series versions. The MS-500 has 18 digital
channels and 500-MHz bandwidth with a 2-GS/s maximum sampling rate.
The MS-500-36 also provides 500-MHz bandwidth but a 1-GS/s maximum
sampling rate and half the memory length when both 18-channel pods
are used. A third model, the MS-250, has 250-MHz bandwidth, a
1-GS/s maximum sampling rate, and only 10 Mpoints of memory per
channel vs. 50 Mpoints for the MS-500 and MS-500-36.
A variety of standard logic family thresholds is selectable, and
you also can program custom threshold values as required. Only one
threshold value may be selected per logic pod for Agilent,
Yokogawa, and LeCroy MSOs. Tektronix supports per-channel threshold
selection or programming.
In addition to these specific hardware differences, all MSO
architectures have a seam between the analog and added-on digital
channels. A simplified block diagram identifies an MSO’s various
parts but not details of their interactions (Figure 2). How much
you notice the seam and what problems it causes will depend on the
particular model of MSO and how you are using it. Many technical
aspects could be discussed, but a few of the more fundamental are
highlighted here.
Figure 2. Simplified MSO Block Diagram
Courtesy of Yokogawa
Click here to see larger image |
Mixed Sampling Rates
For example, how does an MSO handle mixed sampling rates? If you
are simultaneously displaying analog channels and digital channels,
what happens when you increase the analog sampling rate to be
greater than the maximum digital sampling rate? This problem is
common to Tektronix, Agilent Infiniium, and LeCroy MSOs. Yokogawa’s
DL9710L maintains the same maximum sampling rates for the analog
and digital channels as well as a common 6.25-MW memory length
across all channels.
MSOs always acquire the same amount of time for analog and digital
channels. One way to make the operation of features like zooming
appear consistent is to follow Yokogawa’s approach and simply run
both digital and analog channels at the same rates and with the
same memory lengths. Alternatively, if the sampling rates are
different, so too will be the amounts of memory used.
Agilent’s Infiniium 8000 Series MSO samples digital channels at a
maximum 1-GS/s rate and analog channels at either 2 GS/s or 4 GS/s.
The 6000 Series MSO samples eight channels of one logic pod at 2
GS/s or more than eight channels at 1 GS/s. The 6000 Series shares
memory between analog and digital channels, but the Infiniium 8000
does not. For both scope series, equal amounts of time are captured
on digital and analog channels, and the relationship between analog
and digital memory lengths is automatically adjusted as required.
In Tek’s MSO4000 Series, digital channels are acquired at a maximum
500-MS/s sampling rate. The MSO4104 has a maximum 5-GS/s analog
channel sampling rate. The maximum memory length is 10-MW per
channel regardless of type.
However, not all the digital memory length can be used at high
time-base settings if analog channels also are being acquired. Only
1 MW of digital data can be acquired at 500 MS/s during the 2 ms it
takes to fill the 10-MW memory associated with an analog channel
running at 5 GS/s. Mixed-signal acquisition cannot use all of the
10-MW digital channel memory at sample rates above 500 MS/s.
LeCroy’s MS-500 Logic Pod inputs are sampled at a maximum of 2
GS/s. The WaveSurfer Xs and WaveRunner Xi, the host instruments for
the
MS-500 option, can have analog channel sampling rates as high as 5
GS/s or 10 GS/s, respectively.
Were you to simultaneously display analog channels sampled at 5
GS/s and digital channels sampled at 500 MHz, what would you see?
Answering this question requires a slight digression. Each of the
four manufacturer’s MSOs combines changes in sampling rate,
acquisition memory length, and horizontal magnification to arrive
at a composite maximum time-base rate as high as 200 ps/div.
A 200-ps/div time-base setting corresponds to only one sample per
division at a 5-GS/s rate. The other 99% of the waveform is
interpolated. Newer DSOs that use XGA displays generally display
100 points per division at the highest time-base setting. On the
basis of 100 points/div, the fastest unexpanded time-base rate for
MSOs running at a 5-GS/s rate is 20 ns/div.
This time base corresponds to a 1,000-point acquisition or 800
points for Agilent because of the maximum 4-GS/s sampling rate.
Longer acquisitions require more time to complete, naturally
limiting the waveform update rate. When the captured data is
compressed for display, the time-base rate must be scaled
accordingly. For example, to display all of a 1-Mpoint acquisition
made at 5 GS/s requires a 20-µs/div time-base setting. The waveform
update rate under these conditions can never be greater than
5,000/s.
So, at a maximum 20-ns/div time-base setting, Tek’s MSO4104 digital
channels will display 10 samples per division. Agilent’s Infiniium
sampled at 1 GS/s presents 20 points. LeCroy’s digital channels and
those from the Agilent 6000 Series sampled at 2 GS/s, 40 points and
Yokogawa scopes at 2.5 GS/s, 50 points. A number of artifices such
as interpolation or repeated sample values can be used to connect
the real samples at this and faster time-base settings.
Skew Among Channels
All modern DSOs, including the major manufacturers’ MSOs, allow the
analog channels to be deskewed. Either by recalling probe- and
channel-specific values or entering timing corrections manually,
you can null differences in propagation delay across all four input
channels and probes. In contrast, some MSOs do not support digital
channel deskew.
According to Mike Hertz, field applications engineer at LeCroy,
"Both the WaveRunner and WaveSurfer allow deskew control between
the digital channels and analog channels with a resolution of 0.5
ps. Each of the analog channels has its own deskew control located
in the channel menu. For example, the user could deskew channel 1
to +2.4 ns, channel 3 to -1.5 ps, and channel 4 to +100.5 ps
relative to the digital channels.
"The digital channels are already matched and do not need to be
deskewed relative to each other. Any variation in skew between
these matched channels is negligible compared to the timing
resolution with which the timing edges are acquired," he explained.
Yokogawa’s Joseph Ting, product manager at the company’s Test and
Measurement Division, said, "In the DL9710L, skew between logic
channels is negligible. However, skew between the analog and logic
channels typically is around 2 or 3 ns. As a result, the DL9710L
has a skew adjustment feature that allows up to 80 ns of deskew at
10-ps resolution to align the analog and logic channels."
Tektronix specifies skew among digital channels to be 1 ns typical
although the channels are deskewed to a much tighter tolerance as
part of the factory calibration process. This procedure ensures
that the digital channels are aligned for both the acquisition and
trigger systems.
In contrast, Agilent states 2-ns typical, 3-ns maximum
channel-to-channel skew among digital channels. The user has the
ability to adjust analog channel skew and the skew between the
analog and digital channels but not among the digital channels
themselves.
Channel-to-channel skew is important because it directly adds or
subtracts from the timing relationships that actually exist among
your digital signals. For example, if you are trying to understand
a race condition in logic running at 100 MHz, the basic clock rate
and all the signals derived from it are relatively slow.
However, a race is caused by differences in propagation delays and
can easily be 1 ns or less in a 100-MHz system. If the digital
channels probing the affected signals are themselves skewed by 1 ns
or more, there’s no way you can troubleshoot the race condition.
This is a basic limitation. Your most practical option is to use a
couple of accurately time-aligned analog channels to investigate
further.
Separate Acquisition Modes
The Tektronix MSO4104 provides a high-speed MagniVu acquisition
system that automatically captures 10,000 points from each digital
channel centered on the trigger event. Using this feature, you can
examine logic channel timing in more detail, especially transitions
that appear to occur simultaneously when sampled at 500 MS/s. The
highest sampling rate is 16.5 GS/s or a sample every 60.6 ps.
If the 4000 Series digital channel propagation delay stabilities
with time and temperature are sufficiently good, MagniVu becomes a
remarkable tool for looking at signal drift. It can show relative
signal timing changes in great detail.
MSOs simultaneously sample analog and digital channels on edges of
an internal, asynchronous time base. This means that on slow
time-base settings it always is possible that skew can make one
digital signal appear to occur one complete time-base clock ahead
of or after another. The chance of this occurring becomes less as
skew is reduced. MagniVu can minimize this kind of confusion.
Additional troubleshooting insight would be available were MSOs to
support external clocking. Logic state displays imply the existence
of this mode. However, the state information typically is derived
from timing data and not from a separate synchronous acquisition.
The importance of small amounts of channel-to-channel skew becomes
much less when state data is acquired synchronously than when
timing information is acquired asynchronously because the states
are settled when they are sampled.
Both the LeCroy WaveSurfer Xs and WaveRunner Xi accept an external
clock signal on the auxiliary input. So, in theory, the MSOs based
on these instruments could perform true state analysis. Yokogawa’s
DL9000 Series scopes can use an external clock signal on channel 4
to qualify a state trigger formed by a combination of signals on
analog channels 1 through 3. It’s not clear if a variant of this
capability is used to provide true synchronous state acquisition
for the DL9710L logic channels.
Update Rate
It is well understood that a high waveform acquisition rate
improves your chance of acquiring intermittent events. A fast
update rate means that a scope spends more time acquiring and
displaying signals and less time on internal processes such as data
transfer and re-arming. It’s looking at the signal for a greater
proportion of the time so it finds more anomalies. What are the
things that contribute to a high rate or the lack of one?
There’s little that beats dedicated hardware for improving speed.
As Agilent’s Joel Woodward, 6000 and 8000 Series product manager,
explained, "Agilent uses hardware-based serial bus protocol
decoding. Tektronix and LeCroy both have software-based decoding,
and as a result, the update rate is slow for long memory
acquisitions with serial bus decoding. In contrast, Agilent’s
update rate remains at 100,000 waveforms
per second."
Figure 3 shows the type of metastable waveform detail that can only
be captured with a high waveform update rate.
 Figure 3. Infrequent Metastable States Captured Via Fast Waveform
Update Rate
Courtesy of Agilent Technologies |
Yokogawa’s Mr. Ting confirmed that serial bus triggering from logic
channel inputs soon would be available in the DL9710L MSO. Although
this MSO uses hardware serial bus decoding, the update rate is 15
waveforms/s as quoted in the DL9710L datasheet.
While on the subject of serial bus decoding/triggering, remember
that you may not want to use certain digital channel capabilities
even though they are available. For example, most MSOs can decode
serial bus signals from a digital channel. But, digital channels
present only a single-ended connection to the signal source. Some
serial buses such as CAN require differential probing so you need
to use a proper differential probe connected to an analog channel
to directly probe the bus.
MSOs by Another Name
If you like the MSO functionality but perhaps need six analog
channels and more than 16 or even 36 digital channels, why not
create a custom MSO from modular instruments? For example, in
addition to synchronized analog and digital input channels, a
PXI-based system provides synchronized outputs to stimulate the
DUT, very deep on-board memory, high data transfer rates via PXI
Express, and virtually unlimited expansion capability.
National Instruments’ (NI) Scott Savage, product manager for
high-speed digital I/O, explained some of PXI’s capabilities. "The
PXI platform routes the same sample clock to all channels, ensuring
analog and digital synchronization as close as 20 ps. Output
signals share the same sub-nanosecond synchronization, and the
system is scalable to suit your application."
A typical NI system might include a PXI controller and multiples of
the PXI-5152 dual-channel, 2-GS/s digitizer and the PXI-6552
100-MHz, 20-channel digital I/O module depending on the number of
channels needed. Overall test system functionality is defined by a
custom LabVIEW program. Of course, developing your own test program
also means that you can directly address any special computation or
report generation requirements not commonly found in traditional
MSOs.
If your application includes several analog channels that need to
be acquired with more resolution than an MSO’s 8 b, a system based
on GaGe’s Octopus CompuScope might be appropriate. The Octopus is
an eight-channel digitizer that samples input waveforms at up to a
125 MS/s rate with 12- or 14-b resolution. The board supports up to
4-GB of acquisition memory. This combination of numbers of analog
channels, resolution, and memory length simply is not available in
any MSO.
GaGe, like NI, can synchronize digital and analog channels. The
CompuScope CS3200 Digital Input Card with 2 GB of memory provides
up to a 100-MS/s sampling rate for up to 32 channels. Triggering
across both digital and analog channels is supported but generally
not at the same level as in an integrated MSO instrument.
Nevertheless, very large on-board memories reduce the need for
complex trigger conditions.
Conclusion
MSO competition has increased with the recent introduction of
several models. This is good news not only because it gives you
more choice as a consumer, but also because it confirms the
usefulness of this class of instrument. Mixed-signal circuits and
devices are here to stay, and it’s only natural that a type of
instrument has been developed to solve the specific needs of
mixed-signal design and development.
In general, DSOs and MSOs have become exceedingly versatile in the
number and types of acquisition modes, trigger conditions, signal
analysis features, and display capabilities such as the collapsed
buses and separate PreVu and Zoom sections shown in Figure 4.
 Figure 4. State, RS-232, and Parallel Bus Display, PreVu and Zoom
Courtesy of Tektronix |
There are so many features in these products that a reasonable-size
datasheet simply cannot do more than outline the available
functions, even significant new ones. For example, MagniVu is an
MSO feature that has migrated from the range of Tektronix logic
analyzers. Similarly, Agilent’s FPGA dynamic probe feature
originated as a logic analyzer capability.
To appreciate an instrument’s capabilities sufficiently, you need
to use one for a week or two, examining the more challenging
aspects of your mixed-signal application. Read the instrument
datasheet a few times, but keep the manufacturer’s technical help
phone number close at hand. You will need it, especially as you
attempt to understand in detail the limitations of more complex
triggering and acquisition modes.
And, if you still can’t find a suitable set of specifications,
modular instruments may fill the need. You can count on new
capabilities and combinations of features to appear with each
generation of MSO products, extending the range of addressable
applications. Nevertheless, a custom-designed modular instrument
may be just what you require.
当前离线
只不过当时泰克的这个产品很不成功，后来就逐渐淡出示波器舞台了。
