Note: Descriptions are shown in the official language in which they were submitted.
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LOW POWER FLIP-FLOP CIRCUIT
BACKGROUND
Flip-flops may refer to sequential circuits that store either a "high" value
(voltage
high or logic one) or a "low" value (voltage low or logic zero). A flip-flop
may store a next
value that depends on the values of one or more input signals. Conventionally,
a flip-flop
may include data, clock, set, and/or reset input signals.
A Data (conventionally designated D) input signal is typically clocked into
the flip-
flop on receipt of a given clock edge. Set (conventionally designated S) and
Reset
(conventionally designated R) input signals are generally unclocked, meaning
that when the
set or reset signal becomes active (e.g., goes high), the stored value changes
immediately,
without waiting for the arrival of a clock edge. Flop is usually a master-
slave latch structure.
Each latch is active (transparent) during either logic high or logic low phase
(not edge). At
the rising (trigger) edge, the master latch will latch the input and store the
data value, the
slave latch will become active (transparent) and pass the value to the output.
Assume the
active phase for the master latch is 0, then at the falling edge, maser latch
will become active
(transparent) to accept the next value and slave latch will latch what was
latched by the
master latch to continue output the value that was stored in the master latch.
So output will
change only at each triggering edge. An active set signal forces the stored
value
(conventionally designated Q) high, despite the previously stored value. An
active reset
signal forces the stored value Q low, despite the previously stored value. In
set/reset flip-
flops (i.e., flip-flops having both set and reset input signals) the set and
reset signals are
typically restricted such that at most one of them can be active at any given
time. Since flip-
flop is a fundamental building block of modern digital designs, there is
always a need to
minimize its power consumption and area. A flop-flop design is proposed that
would reduce
its power consumption and area compared to conventional designs.
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SUMMARY
The following presents a simplified summary of one or more aspects in order to
provide a basic understanding of such aspects. This summary is not an
extensive overview
of all contemplated aspects and is intended to neither identify key or
critical elements of all
aspects nor delineate the scope of any or all aspects. Its sole purpose is to
present some
concepts of one or more aspects in a simplified form as a prelude to the more
detailed
description that is presented later.
The present disclosure presents examples of flip-flop circuits. An example
flip-flop
circuit may include a flip-flop data input terminal and a flip-flop data
output terminal. The
example flip-flop circuit may further include a clock terminal that provides a
first clock
signal and a second clock signal, wherein the second clock signal is an
inverse of the first
clock signal. In addition, the example flip-flop circuit may include a
passgate coupled
between the flip-flop data input terminal and a first node. The passgate may
include a first
P-channel gate terminal and a first N-channel gate terminal. The first P-
channel gate
terminal and the first N-channel gate terminal may be respectively connected
to the first
clock signal and the second clock signal.
The example flip-flop circuit may further include a passgate inverter coupled
between the first node and a second node. The passgate inverter may include a
first P-
channel transistor, a second P-channel transistor, a first N-channel
transistor, and a second
N-channel transistor. The first P-channel transistor and the second N-channel
transistor may
be connected to the first node. The second P-channel transistor may be
connected to the
second clock signal and the first N-channel transistor may be connected to the
first clock
signal.
The example flip-flop circuit may further include an inverter connected
between the
second node and the flip-flop data output terminal.
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Further still, the example flip-flop circuit may include one or more leakage
compensation units coupled between the first node and the flip-flop data
output terminal.
Each of the leakage compensation units may include a third P-channel
transistor and a third
N-channel transistor.
To the accomplishment of the foregoing and related ends, the one or more
aspects
comprise the features herein after fully described and particularly pointed
out in the claims.
The following description and the annexed drawings set forth in detail certain
illustrative
features of the one or more aspects. These features are indicative, however,
of but a few of
the various ways in which the principles of various aspects may be employed,
and this
description is intended to include all such aspects and their equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosed aspects will hereinafter be described in conjunction with the
appended
drawings, provided to illustrate and not to limit the disclosed aspects,
wherein like
designations denote like elements, and in which:
Fig. 1 is a block diagram illustrating a conventional flip-flop circuit;
Fig. 2 is a block diagram illustrating another conventional flip-flop circuit;
Fig. 3 is a block diagram illustrating another conventional flip-flop circuit;
Fig. 4 is a block diagram illustrating a flip-flop circuit in accordance with
one
embodiment of this invention;
Fig. 5 is a timing diagram illustrating signals of the flip-flop circuit of
Fig. 4; and
Fig. 6 is a block diagram illustrating a flip-flop circuit in accordance with
one or
more embodiments of this inventions.
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DETAILED DESCRIPTION
Various aspects are now described with reference to the drawings. In the
following
description, for purpose of explanation, numerous specific details are set
forth in order to
provide a thorough understanding of one or more aspects. It may be evident,
however, that
such aspect(s) may be practiced without these specific details.
Flip-flop circuits may be designed to include two latches separated by
passgates. For
example, Fig. 1 shows a conventional flip-flop circuit 100 that include a
passgate 102, a
latch 120, a passgate 106, and a latch 122, which are sequentially coupled
together. A
passgate may also be referred to as a pass gate or a transmission gate. In
accordance with
the signal coupled to the N-channel terminal and the P-channel of a passgate,
a passgate
may be either in a closed state (may also be referred to as "connected state")
or an open
state. For example, the passgate 102 of the flip-flop circuit 100 is coupled
between a data
input terminal (shown as "D" in Fig.1) and the latch 120. Another passgate 106
is coupled
between the latch 120 and the latch 122. The latch 120 includes a pair of
cross-coupled
inverters 110 and 112 and a passgate 104 coupled to the inverter 112 in the
feedback. Similar
to the latch 120, the latch 122 includes another pair of cross-coupled
inverters 114 and 116
and a passgate 108 coupled to the inverter 116. As shown in Fig. 1, the clock
signal CK is
inverted to generate inverted clock signal CPB that is provided to respective
N-channel
terminals of the passgates 102, 104, 106, and 108. The inverted clock signal
CPB may be
further inverted to generate clock pulse CP. The clock pulse CP may be
provided to the
respective P-channel terminals of the passgates 102, 104, 106, and 108.
In some examples, the conventional flip-flop circuit of Fig. 1 may function
properly
to generate correct signals. However, the passgates 104 and 108 and the
inverters 112 and
116 may cause high power consumption. The extra power consumption comes from
additional loading on the clock distribution network by the passgate and the
logic operation
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of the inverter. Thus, another conventional flip-flop circuit without the
feedback structure
was proposed.
Fig. 2 is a block diagram illustrating another conventional flip-flop circuit
200. The
flip-flop circuit 200 may include a passgate 202, an inverter 204, a passgate
206, and an
inverter 208. The passgate 202, the inverter 204, the passgate 206, and the
inverter 208 may
be sequentially connected. As show, the flip-flop 200 does not include a
feedback loop
between the node B1 and the node B2. As a result, the voltage at the node B1
may be
unstable due to leakage from or to the passgate 202 and cause incorrect data
values at the
data output terminal of the flip-flop circuit 200 (shown as "A2" and "Q").
Fig. 3 is a block diagram illustrating another conventional flip-flop circuit
300. As
depicted, the flip-flop circuit 300 may include a passgate 302, a passgate
inverter 303, and
an inverter 312. In some examples, the passgate 302, the passgate inverter
303, and the
inverter 312 may be sequentially connected. The passgate inverter 303 may be
connected
between the passgate 302 and the inverter 312. In some examples, the passgate
inverter 303
may include two P-channel transistors 304 and 306 and two N-channel
transistors 308 and
310. A gate terminal of the P-channel transistor 304 and a gate terminal of
the N-channel
transistor 310 may be connected to the node Bl. A gate terminal of the P-
channel transistor
306 may be connected to an inverted clock signal CPB and a gate terminal of
the N-channel
transistor 308 may be connected to a clock signal CK or a clock pulse CP.
Further, a source terminal or a drain terminal of the P-channel transistor 304
may be
connected to a supply terminal VDD. A source terminal or a drain terminal of
the N-channel
transistor 310 may be connected to a ground terminal. The P-channel transistor
306 and the
N-channel transistor 308 may be connected via the source terminals or the
drain terminals
thereof and may be further connected to the node B2.
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The flip-flop circuit 300 may lead to lower power consumption relative to the
flip-
flop circuit 200. Further, in a time interval when the clock pulse CP or clock
signal CK is
low ("0") and the inverted clock signal CPB is high ("1"), leakage current
from the P-
channel transistors 304 and 306 may cause the voltage at the node B2 to
increase; however,
leakage current from the N-channel transistors 308 and 310 may cause the
voltage at the
node B2 to decrease. As such, the voltage at the node B2 may be stabilized for
a period. The
period may be extended with additional capacitance. However, the voltage at
the node B1
may be relatively unstable as there is no feedback structure to stabilize the
voltage at the
node Bl.
Fig. 4 is a block diagram illustrating a flip-flop circuit 400 in accordance
with one
embodiment of this invention. As depicted, the flip-flop circuit 400 may
include a passgate
402, a leakage compensation unit 404, a passgate inverter 406, and an inverter
408. The
passgate 402, the passgate inverter 406, and the inverter 408 may be
sequentially connected.
In other words, the passgate 402 may be connected between a flip-flop data
input terminal
and a first node Bl. The passgate inverter 406 may be connected between the
first node B1
and a second node B2. The inverter 408 may be connected between the second
node B2 and
a flip-flop data output terminal A2/Q. The leakage compensation unit 404 may
be connected
parallel to the passgate inverter 406 and the inverter 408 between the flip-
flop data output
terminal A2/Q and the first node Bl.
In some examples, a P-channel terminal of the passgate 402 may be coupled to
the
clock pulse CP signals and a N-channel terminal of the passgate 402 may be
coupled to the
inverted clock signals CPB.
Similar to the passgate inverter 306, the passgate inverter 406 may also
include a P-
channel transistor 410, a P-channel transistor 412, a N-channel transistor
414, and a N-
channel transistor 416. In some examples, the P-channel transistor 410, the P-
channel
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transistor 412, the N-channel transistor 414, and the N-channel transistor 416
may be
sequentially connected. A gate terminal of the P-channel transistor 410 and a
gate terminal
of the N-channel transistor 416 may be connected to the first node Bl. A
source or drain
terminal of the P-channel transistor 410 may be connected to a supply terminal
VDD; a
source or drain terminal of the N-channel transistor 416 may be connected to a
ground
terminal.
Further to the examples, a gate terminal of the P-channel transistor 412 may
be
connected to the inverted clock signal CPB and a gate terminal of the N-
channel transistor
414 may be connected to the clock pulse CP. The P-channel transistor 412 and
the N-channel
transistor 414 may be connected with the second node B2 via the source or
drain terminals.
Unlike the flip-flop circuit 300, the flip-flop circuit 400 may include at
least one
leakage compensation unit 404 connected between the first node B1 and the flip-
flop data
output terminal A2/Q. In at least one example, the leakage compensation unit
404 may
include a P-channel transistor 418 and a N-channel transistor 420 that may be
sequentially
connected. Gate terminals of the P-channel transistor 418 and the N-channel
transistor 420
may be connected to the flip-flop data output terminal A2/Q. A source or drain
terminal of
the P-channel transistor 418 may be connected to the first node Bl.
In a time interval when the clock pulse CP is high ("1") and the inverted
clock signal
CPB is low ("0'), leakage current from the passgate 402 may cause the voltage
at the first
node B1 to increase. Thus, the voltages at the first node B1 and the flip-flop
data output
terminal A2/Q may no longer be equal, which may further cause leakage at the
leakage
compensation unit 404. The leakage at the leakage compensation unit 404 may
then decrease
the voltage at the first node Bl. Thus, the voltage at the first node B1 may
be adjusted to a
correct value.
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Similarly, when the leakage current from the passgate 402 cause the voltage at
the
first node B1 to decrease, the voltages at the first node B1 and the flip-flop
data output
terminal A2/Q may no longer be equal. The leakage at the leakage compensation
unit 404
may increase the voltage at the first node Bl. The voltage at the first node
B1 may then be
similarly adjusted to a correct value.
Fig. 5 is a timing diagram illustrating signals of the flip-flop circuit of
Fig. 4.
As depicted, prior to time point Ti, due to leakage current from the passgate
inverter
406, voltage at the node B2 may drop gradually till the time point Ti. At time
point T2, the
clock signal CK and the clock pulse CP are high and the inverted clock signal
CPB is low,
the leakage current at the passgate 402 may cause the voltage at the first
node B1 to decrease.
However, the difference of voltages at the first node B1 and the flip-flop
data output terminal
A2/Q may cause leakage at the leakage compensation unit 404 and further
prevent the
voltage at the first node B1 from dropping (as shown in dotted line between T2
and T3).
Thus, the voltage at the first node B1 may be maintained as high from the time
point T2 to
the time point T3 as illustrated.
Similarly, between time points T3 and T4, due to leakage current from the
passgate
inverter 406, voltage at the node B2 may rise gradually till time point T4.
Further, between time points T5 and T6, the clock signal CK and the clock
pulse CP
are high and the inverted clock signal CPB is low, the leakage current at the
passgate 402
may cause the voltage at the first node B1 to increase. The difference of
voltages at the first
node B1 and the flip-flop data output terminal A2/Q may cause leakage at the
leakage
compensation unit 404 and further prevent the voltage at the first node B1
from increasing
(as shown in dotted line between T5 and T6).
Fig. 6 is a block diagram illustrating a flip-flop circuit 600 in accordance
with one
or more embodiments of this inventions.
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As depicted, the flip-flop circuit 600 may include similar components as the
flip-
flop circuit 400 in accordance with Fig. 4. The flip-flop circuit 600 may
include one or more
leakage compensation units 604. For example, the leakage compensation units
may be
connected sequentially, parallelly, or in any arrangement. Each of the leakage
compensation
units 604 may include a P-channel transistor and a N-channel transistor. The
gate terminals
of the P-channel transistor and the N-channel transistor may be connected
together to the
first node Bl, the flip-flop data output terminal A2/Q, or other leakage
compensation units.
The previous description is provided to enable any person skilled in the art
to
practice the various aspects described herein. Various modifications to these
aspects will be
readily apparent to those skilled in the art, and the generic principles
defined herein may be
applied to other aspects. Thus, the claims are not intended to be limited to
the aspects shown
herein but is to be accorded the full scope consistent with the language
claims, wherein
reference to an element in the singular is not intended to mean "one and only
one" unless
specifically so stated, but rather "one or more." Unless specifically stated
otherwise, the
term "some" refers to one or more. All structural and functional equivalents
to the elements
of the various aspects described herein that are known or later come to be
known to those
of ordinary skill in the art are expressly incorporated herein by reference
and are intended
to be encompassed by the claims. Moreover, nothing disclosed herein is
intended to be
dedicated to the public regardless of whether such disclosure is explicitly
recited in the
claims. No claim element is to be construed as a means plus function unless
the element is
expressly recited using the phrase "means for."
Moreover, the term "or" is intended to mean an inclusive "or" rather than an
exclusive "or." That is, unless specified otherwise, or clear from the
context, the phrase "X
employs A or B" is intended to mean any of the natural inclusive permutations.
That is, the
phrase "X employs A or B" is satisfied by any of the following instances: X
employs A; X
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employs B; or X employs both A and B. In addition, the articles "a" and "an"
as used in this
application and the appended claims should generally be construed to mean "one
or more"
unless specified otherwise or clear from the context to be directed to a
singular form.
