U.S. patent application number 10/445094 was filed with the patent office on 2003-11-06 for method and apparatus to provide a low voltage reference generation.
Invention is credited to Sundaram, Rajesh, Taub, Mase, Tedrow, Kerry.
Application Number | 20030208699 10/445094 |
Document ID | / |
Family ID | 28455211 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030208699 |
Kind Code |
A1 |
Taub, Mase ; et al. |
November 6, 2003 |
Method and apparatus to provide a low voltage reference
generation
Abstract
A method and apparatus to provide a low voltage reference
generation. The apparatus includes a reference voltage generator to
receive a first input voltage signal and output a reference voltage
signal. A voltage level detector electrically coupled to the
reference voltage generator to receive the reference voltage signal
and also receive a second input voltage signal. The voltage level
detector compares the second input voltage signal to the reference
voltage signal for generating an output based on the compared
signals.
Inventors: |
Taub, Mase; (Elk Grove,
CA) ; Sundaram, Rajesh; (Fair Oaks, CA) ;
Tedrow, Kerry; (Folsom, CA) |
Correspondence
Address: |
Peter Lam
BLAKELY, SOKOLOFF, TAYLOR & ZAFMAN LLP
Seventh Floor,
12400 Wilshire Boulevard
Los Angeles
CA
90025
US
|
Family ID: |
28455211 |
Appl. No.: |
10/445094 |
Filed: |
May 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10445094 |
May 23, 2003 |
|
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09746119 |
Dec 22, 2000 |
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Current U.S.
Class: |
713/300 |
Current CPC
Class: |
G06F 1/26 20130101; G05F
3/24 20130101 |
Class at
Publication: |
713/300 |
International
Class: |
G06F 001/26 |
Claims
What is claimed is:
1. An apparatus comprising: a reference voltage generator to
receive a first input voltage signal and output a reference voltage
signal; and a voltage level detector electrically coupled to the
reference voltage generator to receive the reference voltage signal
and to receive a second input voltage signal for comparing the
second input voltage signal to the reference voltage signal and
generating an output based on the compared signals.
2. The apparatus of claim 1, wherein the voltage level detector
further comprises: a first terminal to receive the second input
voltage signal; a second terminal to receive the reference voltage
signal; and circuitry electrically coupling the first terminal and
the second terminal to an output.
3. The apparatus of claim 1, wherein the reference voltage signal
has a voltage potential that is lower than the voltage potential of
the first input voltage signal.
4. The apparatus of claim 1, wherein the voltage level detector is
a differential amplifier.
5. The apparatus of claim 1, wherein the reference voltage
generator further comprises: a plurality of transistors, wherein
all the transistors are electrically coupled in series, the gate
and drain of at least one transistor electrically coupled to a
differential amplifier, the source of at least one transistor
electrically coupled to a ground, and at least one transistor with
its drain electrically coupled to a voltage supply and its gate
coupled to an input to receive the first input voltage signal.
6. The apparatus of claim 1, wherein the reference generator and
the voltage level detector are part of a flash memory device.
7. The apparatus of claim 1, wherein the reference voltage
generator further includes a plurality of transistors.
8. The apparatus of claim 7, wherein the reference voltage signal
has a voltage potential that is the same as a voltage potential
across each of the plurality of transistors.
9. The apparatus of claim 7, wherein the plurality of transistors
are in a saturation mode.
10. The apparatus of claim 7, further including a voltage supply
for providing a saturation current to the plurality of
transistors.
11. The apparatus of claim 7, wherein current for the plurality of
transistors is supplied by a voltage supply.
12. The apparatus of claim 7, wherein the reference voltage signal
may be coupled to the gate and drain of any one of the transistors
from the plurality of transistors.
13. The apparatus of claim 7, wherein each of the transistors in
the plurality of transistors includes similar electrical
criteria.
14. A method for generating a low reference voltage comprising:
receiving a first input voltage signal; processing the received
first input voltage signal to generate a reference voltage signal,
wherein the reference voltage signal has a voltage potential that
is lower than the voltage potential at the first input voltage
signal; and comparing the reference voltage signal to a second
input voltage signal for generating an output.
15. The method of claim 14, further comprising using a voltage
supply to supply current to a circuit that produces the reference
voltage signal.
16. The method of claim 14, wherein processing further comprising:
using a plurality of transistors coupled in series; applying the
first input voltage signal to at least one transistor; and
distributing the voltage potential from the first input voltage
signal equally over the plurality of transistors to output the
reference voltage signal such that the reference voltage signal has
the same voltage potential as the voltage potential across at least
one of the transistors.
17. The method of claim 14, further comprising providing a
saturation current to a plurality of transistors.
18. The method of claim 14, wherein comparing further comprising:
receiving the reference voltage signal; receiving the second input
voltage signal; and determining whether the second input voltage
signal is higher or lower than the reference voltage signal.
19. The method of claim 18, further comprising applying the second
input voltage signal to an electronic part if the voltage potential
of the second input voltage signal is higher than the voltage
potential of the reference voltage signal.
20. A digital processing system comprising: a memory; and a
processor to receive a first input voltage signal, to process the
received first input voltage signal to generate a reference voltage
signal, wherein the reference voltage signal has a voltage
potential that is lower than the voltage potential at the first
input voltage signal, and to compare the reference voltage signal
to a second input voltage signal for generating an output.
21. The digital processing system of claim 20, wherein the
processor is to use a voltage supply to supply current to a circuit
that produces the reference voltage signal.
22. The method of claim 20, wherein the processor is to use a
plurality of transistors coupled in series, is to apply the first
input voltage signal to at least one transistor, and is to
distribute the voltage potential from the first input voltage
signal equally over the plurality of transistors to output the
reference voltage signal such that the reference voltage signal has
the same voltage potential as the voltage potential across at least
one of the transistors.
23. The method of claim 20, wherein the processor is to receive the
reference voltage signal, is to receive the second input voltage
signal, and is to determine whether the second input voltage signal
is higher or lower than the reference voltage signal.
24. The method of claim 23, wherein the processor is to apply the
second input voltage signal to an electronic part if the voltage
potential of the second input voltage signal is higher than the
voltage potential of the reference voltage signal.
Description
FIELD OF INVENTION
[0001] The present invention relates generally to voltage
generators. More particularly, the present invention relates to a
method and apparatus to provide a low voltage reference
generation.
BACKGROUND OF THE INVENTION
[0002] A reference voltage generator is a device that is powered by
an input voltage and outputs a reference voltage to compare with
another voltage. Prior art reference voltage generators use
constant voltage input for supplying power to the voltage reference
generation circuit. The same constant voltage input is also used
for generating the voltage reference.
[0003] A problem with this approach is that current technology
devices supply different voltage values that vary with time. The
current voltage reference generators are limited in their operation
since they can only operate under one constant voltage value and
need to be redesigned for a different voltage value. Another
problem with using same constant voltage input for both supplying
current to the circuit and generating a voltage reference is that
it loads the voltage potential of the voltage input by having to
perform two functions. This results in producing a voltage
reference that varies highly with distribution of input voltage
through the circuit.
[0004] Prior art reference voltage generators also provide a
constant output reference voltage irrespective of changes to the
input voltage. A problem with this approach is that it is only
applicable to a very limited number of electronic devices that
support the constant output reference voltage. Thus this approach
may not be modified to apply to parts that do not accept the
produced constant reference voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The features and advantages of the present invention are
illustrated by way of example and not intended to be limited by the
figures of the accompanying drawings in which like references
indicate similar elements and in which:
[0006] FIG. 1 shows an exemplary digital processing system in which
the present invention can be implemented;
[0007] FIG. 2 illustrates a diagram to show a minimum voltage
operating range for an electronic device according to one
embodiment;
[0008] FIG. 3 shows a circuit for generating a low voltage
reference according to one embodiment;
[0009] FIGS. 4a and 4b illustrate diagrams to show a minimum
voltage operating range and corresponding circuit for a 2V
electronic part according to one embodiment; and
[0010] FIG. 5 shows a circuit for producing a voltage reference
signal for a 3V electronic part according to one embodiment.
DETAILED DESCRIPTION
[0011] A method and apparatus to provide a low voltage reference
generation is described. Apparatus includes a reference voltage
generator to receive a first input voltage signal and output a
reference voltage signal. A voltage level detector electrically
coupled to the reference voltage generator to receive the reference
voltage signal and also receive a second input voltage signal. The
voltage level detector compares the second input voltage signal to
the reference voltage signal for generating an output based on the
compared signals.
[0012] The reference voltage generator includes an internal circuit
comprising a plurality of transistors and a voltage supply. The
voltage supply, separate from the first input voltage signal, is
used to power the plurality of transistors. An advantage of having
a separate voltage supply is that the internal circuit draws
current only from the voltage supply and not from the first input
voltage signal. This allows construction of a low power consuming
first input voltage signal and reduces the overall circuit power
consumption.
[0013] Another advantage of having a separate voltage supply is
that the first input voltage signal is left untouched. This allows
the first input signal to retain most of its power and produce the
reference signal with very low variation across process and
temperature skews. Yet another advantage of having a separate
voltage supply is that the reference voltage produced corresponds
to changes in various first input signals and is highly independent
of the power supply that powers the circuit.
[0014] One of the uses for generating a reference voltage signal
having a low voltage potential is to compare it with the second
input voltage signal known as a program voltage signal or "Vpp", of
an electronic part. Electronic parts, such as flash devices have a
specified voltage range for safe operation. The specified voltage
range includes an optimal operating range and a minimum operating
range. The electronic part will be damaged if operating below the
minimum voltage operating range.
[0015] The function of a voltage level detector is to use the
reference voltage signal and compare it to an actual Vpp voltage
level. The voltage level detector is to apply only Vpp values that
are above the minimum operating range of the electronic part for
its safe operation. Vpp values in the minimum operating range are
low values, a low voltage reference is used to compare these
values.
[0016] FIG. 1 shows an exemplary digital processing system 100 in
which the present invention can be implemented. Referring to FIG.
1, digital processing system 100 includes a bus or other
communication means 101 for communicating information, and a
central processing unit (CPU) 102 coupled with bus 101 for
processing information.
[0017] CPU 102 includes a control unit 131, an arithmetic logic
unit (ALU) 132, and several registers 133, which are used to
process information and signals. The circuit of the present
invention for generating a very low voltage reference may be
implemented within ALU 132. Furthermore, another processor 103 such
as, for example, a coprocessor, can be coupled to bus 101 for
additional processing power and speed.
[0018] Digital processing system 100 also includes a main memory
104, which may be a random access memory (RAM) or some other
dynamic storage device that is coupled to bus 101 for storing
information or instructions (program code), which are used by CPU
102 or processor 803. Main memory 104 may also be to store
temporary variables or other intermediate information during
execution of instructions by CPU 102 or processor 103. Digital
processing system 100 also includes static memory 106, read only
memory (ROM), and/or other static storage devices that are coupled
to bus 101, for storing static information or instructions for CPU
102 or processor 103. A mass storage device 107 which may be a
hard, floppy, or optical disk drive can be coupled to bus 101 for
storing information and instructions for digital processing system
100.
[0019] A display 121 such as a cathode ray tube (CRT) or liquid
crystal display (LCD) can be coupled to bus 101. Display device 121
displays information or graphics to a user. Digital processing
system 100 can interface with display 121 via display circuit 105.
A keyboard input 122, or other alphanumeric input device may also
be coupled to bus 101 for communicating information and command
selections to CPU 102. A cursor control 123 such as a mouse, a
trackball, or cursor direction keys maybe coupled to bus 101 for
controlling movement of an object on display 121. A hard copy
device 124 such as a laser printer may be coupled to bus 101 for
printing information on paper, film, or some other like medium. A
number of input/output devices such as a sound recording and
playback device 125 may also be coupled bus 101.
[0020] FIG. 2 illustrates a diagram 200 to show a minimum voltage
operating range for an electronic part according to one embodiment.
As discussed previously, an electronic part includes an optimal
voltage operating range and a minimum voltage operating range. A
program voltage value, "Vpp", within the electronic part's optimal
voltage operating range may be applied to the electronic part for
its optimal performance. A Vpp value lower than the optimal voltage
operating range and within the minimum voltage operating range may
also be applied to the electronic part for its safe operation.
Applying a Vpp value lower than the minimum voltage operating range
damages the electronic part. A voltage reference is selected within
the minimum voltage operating range for comparing actual Vpp
voltage level values and ensuring that only actual Vpp voltage
level values that are above the minimum voltage operating range are
applied to the electronic part.
[0021] Referring to FIG. 2, Vpp optimal and minimum voltage
operating range values are obtained from the specifications for the
electronic part. The optimal and minimum voltage operating vary for
every electronic part.
[0022] The Vpp minimum voltage operating range includes an upper
limit voltage 20 and a lower limit voltage 22. The electronic part
may be operated safely by applying Vpp values above the upper limit
voltage 20 to the electronic part. Applying Vpp values below the
lower limit voltage 22 damages the electronic part.
[0023] Vpp values that are between the upper limit voltage 20 and
lower limit voltage 22 may also be applied to the electronic part.
However it is recommended to include a safety margin by applying
Vpp values that are above the lower limit voltage 22 for safe
operation of the electronic part.
[0024] If Vpp is at or above the upper limit voltage 20 then the
electronic part to which Vpp is being applied is unlocked and Vpp
is applied to the electronic part. If Vpp is at or below the lower
limit voltage 22 then the part is locked and Vpp is not applied to
the electronic part. Alternatively, if Vpp value is below the
safety margin, then the part is locked and Vpp is not applied to
the electronic part.
[0025] "V.sub.ref" is a low voltage reference signal that is
selected within the minimum voltage operating range for comparing
actual Vpp voltage level values. A V.sub.ref value may be selected
at any point between the upper limit voltage 20 and the lower limit
voltage 22. Typically, a V.sub.ref value is selected at a midpoint
26 between the upper limit voltage 20 and the lower limit voltage
22. Midpoint 26 acts as the safety margin and is used for making a
decision whether to lock or unlock the part in advance of reaching
the lower limit voltage 22. Thus, a Vpp value above the selected
V.sub.ref value is applied to the electronic part and a Vpp value
below the selected V.sub.ref value is not applied to the electronic
part.
[0026] FIG. 3 shows a circuit 300 for generating the low voltage
reference signal according to one embodiment. Referring to FIG. 3,
circuit 300 includes a plurality of transistors M1-Mn that are part
of a reference voltage generator, a first input signal "V1", a
voltage reference signal "V.sub.ref", a voltage level detector, a
second voltage input signal "Vpp", and a final output. For purposes
of explanation, transistors M1-Mn are depleted mode
negative-channel metal Oxide semiconductors (NMOS) transistors. A
depleted mode NMOS transistor has a threshold voltage between -150
millivolts and +150 millivolts. Alternatively, transistors M1-Mn
may be implemented with other types of transistors. Combined
circuitry 300 may be a part of ALU 132 used by CPU 102.
[0027] The inputs, outputs, and associated circuitry for the
circuit 300 will now be described. Voltage potential V1 is
generated through use of circuitry or a voltage generating source.
The voltage potential at V1 is typically 1.33V for standard
electronic part such as a flash device. Alternatively, the voltage
potential at V1 varies with the type of electronic part to which it
is being applied.
[0028] A voltage reference generator 30 is coupled to the voltage
potential V1 to receive the first input voltage signal. The voltage
reference generator 30 includes an internal circuit comprising a
plurality of transistors M1-Mn. The transistors are electrically
coupled in series, have the same size within a tolerance, contain
the same electrical criteria, and are in a saturation mode.
Alternatively, the transistors may be coupled in any combination to
produce the selected Vref that is within the electronic part's
minimum voltage operating range.
[0029] The drain of transistor M1 is coupled to a voltage potential
"Vcc". Vcc is a voltage supply for the circuit 300, which provides
a saturation current for transistors M1-Mn. The gate of transistor
M1 is coupled to V1 to receive the first input voltage signal, and
the source of transistor M1 is coupled to drain of transistor
M2.
[0030] The gate and drain of transistor M2 is coupled to a voltage
level detector 32 for outputting the selected Vref. Alternatively,
voltage level detector 32 is coupled to gate and drain of any
transistor from the plurality of transistors to output the selected
V.sub.ref. For example, if the voltage potential between the drain
of transistor M2 and ground is similar to the selected V.sub.ref,
then voltage level detector 32 is coupled to M2. However if
selected V.sub.ref value is lower than voltage potential between
the drain of transistor M2 and ground, then the voltage level
detector is coupled to a transistor Mn that has a voltage potential
lower than M2 and similar to the selected V.sub.ref.
[0031] The source of transistor M2 is coupled to either drain of
transistor Mn or ground depending upon number of transistors
required. The number of transistors required depends upon voltage
potential V1 and selected V.sub.ref. For example for a given V1 if
two transistors M1, and M2 are sufficient to produce a voltage
potential across at least one transistor that is similar to the
selected V.sub.ref, then source of transistor M2 is coupled to
ground. However if the selected V.sub.ref is lower than voltage
potential across M1 and M2, then N number of transistors are added
to produce the selected V.sub.ref. In such case, source of
transistor M2 is coupled to drain of transistor Mn, source of
transistor Mn is coupled to ground, and gate of Mn is coupled to
source of M2. FIG. 4b shows a circuit including two transistors,
and FIG. 5 shows a circuit including more than two transistors.
[0032] The voltage level detector 32 coupled to transistor M2 is a
differential amplifier. Alternatively, the voltage level detector
32 can be other type of circuitry that performs the same function
as that of a differential amplifier. The negative terminal of the
differential amplifier 32 receives V.sub.ref. The positive terminal
of the differential amplifier 32 is coupled to Vpp for receiving
the second input voltage signal, also known as actual Vpp voltage
signal. The differential amplifier has an internal circuit, which
compares the received Vpp is signal with the received
V.sub.ref.
[0033] An output 34 is coupled to the differential amplifier 32.
The output 34 is produced by the differential amplifier as a result
of the Vpp comparison made using V.sub.ref. The output is a "1" if
the received Vpp signal is above the received V.sub.ref value, and
a "0" if the received Vpp signal is below the received V.sub.ref
value. An output of "1" results in the differential amplifier 32
unlocking the electronic part and applying the received Vpp to the
electronic part. A value of "0" results in the differential
amplifier 32 locking the electronic part and preventing Vpp from
being applied to the electronic part, thereby securing the
electronic part from being damaged.
[0034] In one embodiment and one cycle of operation, V.sub.ref is
selected for an electronic part that is within the electronic
part's Vpp minimum voltage operating range. A circuit 300 is
designed to receive a first input signal and produce the determined
V.sub.ref signal. The circuit 300 includes a number of transistors,
wherein the number is selected such that voltage potential across
at least one transistor is similar to the selected V.sub.ref. The
circuit 300 also includes a voltage supply Vcc that has a higher
voltage potential than the first input signal. Voltage supply Vcc
provides a saturation current to the transistors in the reference
voltage generator 30 and places the transistors in a saturation
mode.
[0035] A transistor is in a saturation mode when the gate and drain
of the transistor is coupled together. When a transistor is in a
saturation mode, the voltage between the drain and the source of
the transistor is greater than or equal to the difference between
the voltage potential between the gate and source of the transistor
and its threshold voltage as indicated in equation (1) below:
Vds.gtoreq.Vgs-Vt (1)
[0036] Where Vds=Voltage between drain and source of a transistor,
Vgs=Voltage between gate and source of the transistor, and
Vt=Transistor threshold voltage.
[0037] Alternatively, a transistor is in saturation mode when its
gate receives an input voltage, and drain receive a Vcc voltage,
where the Vcc voltage potential is higher than the difference
between the input voltage and the threshold voltage.
[0038] The transistors in saturation receive saturation current
from Vcc. The relationship between the saturation current and
voltage potential across a transistor in saturation mode is
explained in equation (2) shown below:
I.sub.ds=(.beta./2)*(Vgs-Vt).sup.2 (2)
[0039] Where .beta. is a constant determined by equation (3) shown
below:
.beta.=.mu.*C.sub.ox*W/L (3)
[0040] Where .mu.=Effective surface mobility of carrier inside a
channel of a transistor, W=Width of the transistor, and L=Length of
the transistor.
[0041] Equation (2) may be solved to getting the voltage drop
across each transistor as shown in equation (4) shown below:
Vgs=[2/.beta.*Sqrt(Ids)]+Vt (4)
[0042] Where Vt is a constant threshold voltage.
[0043] Since the width, length, effective surface mobility, all
electrical criteria, and saturation current Ids for all the
transistors is the same, the voltage drop Vgs across each
transistor is also the same. Thus the input voltage is equally
divided over the number of transistors in the reference voltage
generator 30.
[0044] The transistor having a voltage potential similar to
V.sub.ref is coupled to the voltage level detector 32. The voltage
level detector 32 compares Vpp to V.sub.ref and applies Vpp values
that are above V.sub.ref to the electronic part.
[0045] In another embodiment and another cycle of operation, a
circuit 300 is designed to produce any desired V.sub.ref voltage
signal. The circuit includes the plurality of transistors M1-Mn
that are in saturation mode and coupled to a voltage supply for
receiving a saturation current. A transistors having the desired
V.sub.ref voltage between its source and ground is coupled to a
differential amplifier. V.sub.ref signal is used to compare any
second input signal received by the differential amplifier. The
comparison results in allowing the received second input signal to
pass as the output signal if the received second input signal has a
voltage potential that is higher than the V.sub.ref signal.
[0046] FIGS. 4a and 4b illustrate diagrams to show a minimum
voltage operating range for a 2V electronic part and a
corresponding circuit according to one embodiment.
[0047] Referring to FIG. 4a, the optimal voltage operating range
for a 2V electronic part is from 1.65V to 1.95V. The minimum
voltage operating range for a 2V electronic part is from 0.4V-0.9V.
The minimum voltage operating range for a 2V electronic part
includes an upper limit 40 having a voltage potential of 0.9V and
lower limit 42 having a voltage potential of 0.4V.
[0048] Applying a Vpp above the upper limit 40 of 0.9V operates the
2V electronic part safely. Applying a Vpp below the lower limit 40
of 0.4V damages the 2V electronic part. As shown in FIG. 4a, a
V.sub.ref range 44 exists between 0.4-0.9V. A V.sub.ref may be
selected at any point within the V.sub.ref range 44. The V.sub.ref
range 44 includes the lowest values allowed by the electronic part
specifications for safe part operation. A V.sub.ref may be selected
at a midpoint 46 for the 2V electronic part. Selecting a midpoint
46 having a value of 0.65V as the V.sub.ref provides a safety
margin by locking the part before Vpp reaches 0.4V lower limit
voltage. Alternatively, a V.sub.ref may be selected at a point
higher than midpoint and closer to the upper limit 40 thereby
achieving a higher safety margin.
[0049] FIG. 4b shows a circuit designed for the standard electronic
part such as a 2V flash device that achieves a V.sub.ref of
approximately 0.65V. The circuit includes a voltage reference
generator 440 comprising two transistors M1 and M2 that are
connected in series, of same size and electrical criteria, and in
saturation.
[0050] The input voltage potential V1 of 1.33V is distributed over
the two transistors to achieve a voltage potential of 0.66V across
each transistor. Transistor M2 is coupled to differential amplifier
442 to output a V.sub.ref value of 0.66V. The differential
amplifier 442 uses the V.sub.ref of 0.66V to compare the current
Vpp. If Vpp is above 0.66V then Vpp is applied to the 2V device.
However if Vpp is less than 0.66V then the part is locked out and
Vpp is not applied.
[0051] FIG. 5 shows a circuit for producing a voltage reference
signal for a 3V electronic part according to one embodiment. As
previously discussed, the midpoint for a 3V electronic part can be
determined similar to the 2V electronic part from specifications
for the 3V electronic part. The midpoint for a 3V electronic part
from specification can be selected at 1.8V. Which means that if the
Vpp in the current circuit is above 1.8V then the part stays
unlocked, and if its below 1.8V then part is locked.
[0052] One embodiment of designing a circuit to produce a reference
signal V.sub.ref for comparing current Vpp is further described. A
voltage reference generator 50 with three transistors M1-M3 is
designed. The gate of the first transistor M1 is coupled to voltage
potential V1 to receive the first input voltage signal of 1.33V.
The received first input signal of 1.33V is distributed equally
across transistors M1, M2, and M3 at 0.443V per transistor.
[0053] The drain of M1 is coupled to voltage supply Vcc and the
source of M1 is is coupled to drain of M2. The gate and drain of M2
is coupled to differential amplifier 52 to output a V.sub.ref. The
source of M2 is coupled to drain of M3. The source of M3 is coupled
to ground, and gate of M3 is coupled to source of M2.
[0054] Since voltage potential V1 is equally distributed at
{fraction (1/3)} per transistor, the transistor M2 is coupled to
the differential amplifier 52 at point "A" which is a V.sub.ref
output, to produce a V.sub.ref output of 0.886V.
[0055] The negative terminal of a differential amplifier 52 is
coupled to transistor M2 to receive the produced V.sub.ref. The
positive terminal of the differential amplifier 52 is coupled to
resistor R2. Resister R2 is coupled to resistor R1 in series which
is coupled to voltage potential Vpp to receive the second input
voltage signal. Since Vpp value of approximately 1.8 is estimated
from specification for a 3V part, the two resistors in series drop
Vpp voltage by half producing an estimated 0.9V. Using of resistors
and dropping estimated Vpp voltage to 0.9V allows a close
comparison with the V.sub.ref 0.886.
[0056] Differential amplifier 52 is coupled at point "A" to achieve
a voltage potential V.sub.ref similar to the estimated Vpp of 0.9.
Alternatively, if a lower value of Vpp is estimated then
differential amplifier would be connected at point "B" to produce a
lower V.sub.ref, i.e. to the gate and drain of M3 thereby achieving
a V.sub.ref of 0.443 instead of 0.886.
[0057] The differential amplifier 52 compares V.sub.ref of 0.886
with the actual Vpp voltage level. A compared Vpp value above
0.886V results in an output 54 of "1" unlocking and applying the
Vpp to the electronic part. A compared Vpp value below 0.886V
results in an output 54 of "0" locking and not applying the Vpp to
the electronic part.
[0058] These and other embodiments of the present invention may be
realized in accordance with these teachings and it should be
evident that various modifications and changes may be made in these
teachings without departing from the broader spirit and scope of
the invention. The specification and drawings are, accordingly, to
be regarded in an illustrative rather than restrictive sense and
the invention measured only in terms of the claims.
* * * * *