Lesson 22 Flip-Flop《电子技术专业英语教程》冯新宇 主编电子工业出版社 www.phei.com.cnUnit8 Digi
tal Logic Circuit《电子技术专业英语教程》2Lesson 22 Flip-FlopBackgroundsText
tour Language in useVocabulary Structure Reading/writing techniq
ues《电子技术专业英语教程》3Terminology multivibrator n.【计】多谐振荡器field effe
ct transistor 【计】场效应晶体管shift register 移位寄存器 Backgrounds
《电子技术专业英语教程》4Text tour Outline Flip-flop Flip-flop’s inventionS
imple flip-flopsClocked flip-flopsThe type of flip-flopsSet–reset
flip-flops (SR flip-flops) Trigger flip-flops (T flip-flops)JK f
lip-flopD flip-flop《电子技术专业英语教程》5Flip-flopIn digital circuits, a
flip-flop is a term referring to an electronic circuit (a bistabl
e multivibrator) that has two stable states and thereby is capabl
e of serving as one bit of memory. Today, the term flip-flop has
come to mostly denote non-transparent (clocked or edge-triggered)
devices, while the simpler transparent ones are often referred t
o as latches; however, as this distinction is quite new, the two
words are sometimes used interchangeably.A flip-flop is usually c
ontrolled by one or two control signals and/or a gate or clock si
gnal. The output often includes the complement as well as the nor
mal output. As flip-flops are implemented electronically, they re
quire power and ground connections.《电子技术专业英语教程》6Flip-flop’s inve
ntionThe first electronic flip-flop was invented in 1918 by Willi
am Eccles and F. W. Jordan. It was initially called the Eccles-Jo
rdan trigger circuit and consisted of two active elements. The na
me flip-flop was later derived from the sound produced on a speak
er connected to one of the back coupled amplifiers outputs during
the trigger process within the circuit. This original electronic
flip-flop——a simple two-input bistable circuit without any dedic
ated clock signal was transparent, and thus a device that would b
e labeled as a "latch" in many circles today.《电子技术专业英语教程》7Simple
flip-flopsSimple flip-flops can be built around a pair of cross-
coupled inverting elements: vacuum tubes, bipolar transistors, fi
eld effect transistors, inverters, and inverting logic gates have
all been used in practical circuits-perhaps augmented by some ga
ting mechanism . The more advanced clocked devices are specially
designed for synchronous systems; such devices therefore ignore i
ts inputs except at the transition of a dedicated clock signal. T
his causes the flip-flop to either change or retain its output si
gnal based upon the values of the input signals at the transition
. Some flip-flops change output on the rising edge of the clock,
others on the falling edge. 《电子技术专业英语教程》8Clocked flip-flopsClock
ed flip-flops are typically implemented as master-slave devices w
here two basic flip-flops (plus some additional logic) collaborat
e to make it insensitive to spikes and noise between the short cl
ock transitions; they nevertheless also often include asynchronou
s clear or set inputs which may be used to change the current out
put independent of the clock.《电子技术专业英语教程》9The type of flip-flops
Flip-flops can be further divided into types that have found com
mon applicability in both asynchronous and clocked sequential sys
tems: the SR ("set-reset"), D ("data" or "delay"), T ("trigger"),
and JK types are the common ones; all of which may be synthesize
d from other types by a few logic gates . The behavior of a parti
cular type can be described by what is termed the characteristic
equation, which derives the "next" (i.e., after the next clock pu
lse) output, Qnext, in terms of the input signal(s) and/or the cu
rrent output, Q.《电子技术专业英语教程》10Set–reset flip-flops (SR flip-flop
s)The fundamental latch is the simple SR flip-flop, where S and R
stand for set and reset respectively. It can be constructed from
a pair of cross-coupled NAND or NOR logic gates. The stored bit
is present on the output marked Q.《电子技术专业英语教程》11Set–reset flip-f
lops (SR flip-flops)Normally, in storage mode, the S and R inputs
are both low, and feedback maintains the Q and outputs in a con
stant state, with the complement of Q. If S is pulsed high while
R is held low, then the Q output is forced high, and stays high
even after S returns low; similarly, if R is pulsed high while S
is held low, then the Q output is forced low, and stays low even
after R returns low. Figure 20-1 shows the symbol for a SR latch.
Figure 20-1 The symbol for a SR latch《电子技术专业英语教程》12Trigger flip
-flops (T flip-flops)If the T input is high, the T flip-flop chan
ges state ("toggles") whenever the clock input is strobed. If the
T input is low, the flip-flop holds the previous value. This beh
avior is described by the characteristic equation:(or, without be
nefit of the XOR operator, the equivalent:
) and can be described in a truth table:《电子技术专业英语教程》13Tr
igger flip-flops (T flip-flops)Figure 20-2 shows T-type flip-flop
. When T is held high, the trigger flip-flop divides the clock fr
equency by two; that is, if clock frequency is 4 MHz, the output
frequency obtained from the flip-flop will be 2 MHz. This ''divide
by'' feature has application in various types of digital counters
. A T flip-flop can also be built using a JK flip-flop (J & K pin
s are connected together and act as T) or D flip-flop (T input an
d Qprevious is connected to the D input through an XOR gate).Figu
re 20-2 T-type flip-flop 《电子技术专业英语教程》14JK flip-flopThe JK flip-f
lop augments the behavior of the SR flip-flop (J=Set, K=Reset) by
interpreting the S=R=1 condition as a "flip" or toggle command.
Specifically, the combination J=1, K=0 is a command to set the fl
ip-flop; the combination J=0, K=1 is a command to reset the flip-
flop; and the combination J = K = 1 is a command to toggle the fl
ip-flop, i.e., change its output to the logical complement of its
current value. Setting J= K = 0 does NOT result in a D flip-flop
, but rather, will hold the current state. To synthesize a D flip
-flop, simply set K equal to the complement of J. The JK flip-flo
p is therefore a universal flip-flop, because it can be configure
d to work as an SR flip-flop, a D flip-flop, or a T flip-flop. NO
TE: The flip flop is positive edge triggered (Clock Pulse) as see
n in Figure 20-3.Figure 20-3 JK flip-flop《电子技术专业英语教程》15JK flip-f
lopThe characteristic equation of the JK flip-flop is:and the cor
responding truth table is:《电子技术专业英语教程》16D flip-flopThe Q output
always takes on the state of the D input at the moment of a risin
g clock edge (or falling edge if the clock input is active low).
It is called the D flip-flop for this reason, since the output ta
kes the value of the D input or Data input, and Delays it by one
clock count. The D flip-flop can be interpreted as a primitive me
mory cell, zero-order hold, or delay line. Figure 20-4 shows D fl
ip-flop. Figure 20-4 D flip-flop 《电子技术专业英语教程》17D flip-flopTruth
table: These flip flops are very useful, as they form the basis f
or shift registers, which are an essential part of many electro
nic devices. The advantage of the D flip-flop over the D-type lat
ch is that it "captures" the signal at the moment the clock goes
high, and subsequent changes of the data line do not influence Q
until the next rising clock edge. An exception is that some flip-
flops have a ''reset'' signal input, which will reset Q (to zero),
and may be either asynchronous or synchronous with the clock.《电子
技术专业英语教程》18Vocabulary Acquisition stimulus margin evaluation anc
illary briefStructureReading/writing techniquesLanguage in use《
电子技术专业英语教程》19Vocabulary《电子技术专业英语教程》20Acquisition in dictionaryTh
e act of acquiring. 获得，取得Something acquired, especially an additi
on to an established category or group. 获得物The process of locatin
g a satellite, guided missile, or moving target so that its track
or orbit can be determined. 搜索，探测《电子技术专业英语教程》21Acquisition in t
extAn acquisition instrument – usually an oscilloscope or logic a
nalyser–is probably the first thing that comes to mind when you t
hink about making electronic measurements. 当进行电子测量时，人们首先想到的很可能是一件
采集仪器——通常是示波器或逻辑分析仪。 《电子技术专业英语教程》22Acquisition in use aircraft ta
rget acquisition空中目标的搜索high-speed data acquisition高速数据采集language
acquisition语言习得technique acquisition技术引进《电子技术专业英语教程》23Stimulus i
n dictionarySomething causing or regarded as causing a response.
刺激因素An agent, an action, or a condition that elicits or accelerat
es a physiological or psychological activity or response. 刺激物《电子
技术专业英语教程》24Stimulus in textThe toolset for digital design charact
erization differs from its counterpart in analog/mixed signal des
ign, but both must include stimulus instruments and acquisition i
nstruments. The signal source, or signal generator, is the stimul
us source that pairs with an acquisition instrument to create the
two elements of a complete measurement solution. 用于数字设计特性评价的测量仪器
和用于模拟/混合信号设计的测量仪器是不一样的，但两者一定都包含激励信号产生仪器和信号采集仪器。信号源（或信号发生器）和采集仪器是构
成一个完整测量解决方案的两大基本组成部分。《电子技术专业英语教程》25Stimulus in use under the sti
mulus of this hopeLight is a stimulus to growth in plants.《电子技术专
业英语教程》26Margin in dictionaryAn edge and the area immediately adja
cent to it; a border. 边缘，边界The blank space bordering the written
or printed area on a page. 空白A limit in a condition or process, b
eyond or below which something is no longer possible or acceptabl
e: 极限the margin of realityhas crossed the margin of civilized beh
avior.《电子技术专业英语教程》27Margin in dictionaryAn amount allowed beyond
what is needed: 余地A measure, quantity, or degree of difference:
差数The minimum return that an enterprise may earn and still pay fo
r itself. 边际收益The border of a leaf. 树叶的边缘《电子技术专业英语教程》28Margin in
dictionaryIn telegraphy, a measure of the ability of the receivi
ng apparatus to copy with timing errors in the received signal.I
n printing, the space surrounding the type area, comprising head,
tail, back and for edge.《电子技术专业英语教程》29Margin in textTo cite ano
ther example, engineers must characterize their emerging designs
to ensure that the new hardware meets design specifications acros
s the full range of operation and beyond. This is known as margin
or limit testing. 举另外一个例子。为了确保新硬件在整个操作范围及该范围之外满足性能设计要求，工程师们必须对即将
完成的设计进行特性评价。这就是所谓的“边缘测试或极限测试”。 《电子技术专业英语教程》30Margin in use by a
comfortable margin 以较大的多数by a narrow margin 以微弱多数by a ... margin
以...之差《电子技术专业英语教程》31Margin in use binding margin装订边continental m
argin大陆边缘current margin工作电流范围, 电流容限design margin设计余量error margin误
差容限《电子技术专业英语教程》32Margin in use low level noise margin低电平噪声容限magn
itude margin幅值裕度noise margin噪声容限, 噪声安全系数nominal margin标称容限peak ma
rgin峰值容限《电子技术专业英语教程》33Evaluation in dictionaryA process to deter
mine whether or not an item of hardware or software can perform a
particular required function or to determine which of two or mor
e items can perform the function best. 评价；鉴定A process to reduce a
n expression to its simplest form or a single value. 计算，求值《电子技术
专业英语教程》34Evaluation in textA signal source is nothing less than t
he cornerstone of almost any instrumentation setup used in hardwa
re design, debug, or evaluation projects 信号源是用于硬件设计、调试、评价工程中的几乎任何
一种测量配置的基础。 《电子技术专业英语教程》35Evaluation in use accomplishment evalua
tion学业成绩评定hazard evaluation危害评价loss evaluation损耗估算evaluation of d
eterminants行列式的求值《电子技术专业英语教程》36Ancillary in dictionarySubordinat
e: 从属的Auxiliary; helping: 辅助的；补充的Something, such as a workbook, t
hat is subordinate to something else, such as a textbook. 附属物《电子
技术专业英语教程》37Ancillary in text It can be very difficult to design a
n instrumentation-quality signal generator, and of course, the time spent designing ancillary test equipment is a costly distraction from the project itself.设计一个仪器级的信号发生器是非常困难的，而且设计辅助设备耗费的时间也将人们的宝贵精力从项目中分散开。《电子技术专业英语教程》38Brief in dictionaryShort in time, duration, length, or extent. 短的Succinct; concise: 简洁的；扼要的：Curt; abrupt. 唐突的《电子技术专业英语教程》39Brief in dictionaryA short, succinct statement. 简短，扼要的陈述A condensation or an abstract of a larger document or series of documents. 概要，摘要《电子技术专业英语教程》40Brief in text Similarly, these fast AWGs with deep memory can generate very brief digital pulses and transients.同样，这些高速、大存储深度的 AWG能够产生非常短暂的数字脉冲和暂态波形。 《电子技术专业英语教程》41Brief in use in brief 简言之; 以简洁的形式make brief of 使简短brief and to the point 简单扼要《电子技术专业英语教程》42Structure《电子技术专业英语教程》43Reading / Writing techniques |
|
