Information
-
Patent Grant
-
6630854
-
Patent Number
6,630,854
-
Date Filed
Monday, January 14, 200222 years ago
-
Date Issued
Tuesday, October 7, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 323 266
- 323 268
- 323 270
- 323 271
- 323 273
- 323 274
- 323 275
- 323 279
- 327 50
- 327 58
- 327 60
- 327 62
- 327 72
- 327 74
- 327 77
- 327 227
- 327 230
- 327 261
- 327 262
-
International Classifications
-
Abstract
The present invention relates a monostable circuit adapted to provide a delay having a length inversely proportional to an input signal, characterized by comprising generating means (21, 22) adapted to generate a signal proportionally to an input signal (Vin) and to a corrective factor (35), comparing means (23) adapted to compare the value of said signal with a prefixed value range (Imin, Imax) and correcting means (24) adapted to correct said corrective factor (35) in the case that the value of said signal is out of said prefixed value range (Imin, Imax).
Description
BACKGROUND OF THE INVENTION
The present invention relates to a controlled voltage monostable circuit.
In some applications a monostable circuit is needed, adapted to generate a pulse, having a time length inversely proportional to a voltage. This voltage needs to control said monostable circuit so that the time length of the pulse can be modified in a large range of time values.
A typical monostable circuit, according to the prior art, such to ensure the request heretofore, foresees a delay element and a memory element connected in feedback configuration.
However the circuit embodiments of such circuits do not guarantee performances, such as precision and consumptions, equal to what is attainable by means of less stringent conditions of the variability of the length of the pulse.
In view of the state of the art described, it is an object of the present invention to avoid the limits and problems of the circuits of the prior art.
SUMMARY OF THE INVENTION
According to the present invention, such object is achieved by a monostable circuit adapted to provide a delay having a length inversely proportional to an input signal, characterized by comprising generating means adapted to generate a signal proportionally to an input signal and to a corrective factor, comparing means adapted to compare the value of said signal with a prefixed value range and correcting means adapted to correct said corrective factor in the case that the value of said signal is out of said prefixed value range.
According to the present invention, such object is also obtained by a method for generating a delay having a length inversely proportional to signal, characterized by comprising the following steps: a) to generate a signal proportionally to an input signal and to a corrective factor; b) to compare the value of said signal with a prefixed value range; c) to correct said corrective factor in the case that said signal is out of said prefixed value range.
Thanks to the present invention it is possible making a monostable circuit having a maximum length of the switching pulse greater than various ranks of the minimum length of said switching pulse.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and the advantages of the present invention will be made evident by the following detailed description of an embodiment thereof, which is illustrated as not limiting example in the annexed drawings, wherein:
FIG. 1
shows a basic scheme of a controlled voltage monostable circuit, according to the prior art;
FIG. 2
shows a schematic circuit of a block of
FIG. 1
;
FIG. 3
shows in greater detail the schematic circuit of
FIG. 2
;
FIG. 4
shows a schematic circuit of the controlled voltage monostable circuit according to the present invention;
FIG. 5
shows in detail the schematic circuit of
FIG. 4
;
FIG. 6
shows an application of the controlled voltage monostable circuit according to the present invention.
DETAILED DESCRIPTION
In
FIG. 1
a basic scheme of a controlled voltage monostable circuit, according to the prior art is shown.
According to what shown in such a Figure, there are noted a first block
1
, and a second block
2
, connected in feedback configuration.
The block
1
is a delay circuit, having a first input
3
for a control voltage Vin, a second input
4
adapted to receive the output of said second block
2
, and an output
5
.
The block
2
is a Set-Reset type flip flop memory circuit, having a first input
6
connected to a line Start, a second input
7
connected to the output
5
of said first block
1
, and an output
8
connected to said second input
4
of said first block
1
.
The output
8
is the output Out of the monostable circuit shown in Figure.
The basic scheme of the block
1
of
FIG. 1
is circuitally shown in
FIG. 2
, wherein it is to be noted that the block
2
is realized by a voltage converter
9
and by a first switch
10
. Said switch
10
is controlled to switch by a first signal In.
The block
2
is formed by a capacitor C, a second switch
11
and a comparator
12
. Said second switch
11
is controlled to switch by the inverted version of said first signal In. Said capacitor C is connected by a side to ground and by the other side to the non inverting terminal of the comparator
12
and to the switch
10
.
The voltage current converter
9
receives the control voltage Vin and it provides a current proportional to said voltage Vin. When the signal Vin controls to close the switch
10
and to open the switch
11
, said current charges the capacitor C. To the terminals of the capacitor C a voltage Vc is present that is compared by the comparator
12
with a reference voltage Vref so as to provide the output signal Out when Vc>Vref.
When the signal In controls to open the switch
10
and to close the switch
11
, the charge contained in said capacitor C discharges toward the ground.
In
FIG. 3
in greater detail the schematic circuit of
FIG. 2
is shown.
The block
1
, besides comprising the voltage current converter block
9
and the switch block
10
, comprises also a block
13
connected to a supply line Vcc.
Particularly, the voltage current converter
9
is realized by a sense amplifier
14
, on the output of which is connected a n channel MOS transistor
15
in source follower configuration and by a resistance R, connected by a side to the inverting terminal of said sense amplifier
14
and to the source terminal of said transistor
15
and to the other side to ground.
The block
13
is realized by means of a couple of p channel MOS transistors
16
and
17
placed in mirror configuration, wherein the transistor in transdiode configuration
16
is connected to the drain terminal of said transistor
15
and the transistor
17
is connected to the switch block
10
.
The block
10
is realized by means of a further couple of p channel MOS transistors
18
and
19
, wherein the first transistor
18
has the gate terminal connected to the signal In, the source terminal to ground and the drain terminal in common with the drain terminal of the second transistor
19
.
Said second transistor
19
has the gate terminal connected with the inverted signal In while the source terminal is connected to the block
2
.
The switch
11
, being part of the block
2
, is realized by a n channel MOS transistor
20
having the gate terminal connected to the inverted signal In, the drain terminal connected to the non inverting terminal of said comparator
12
and with the transistor
19
, and the source terminal to ground.
The way of working of such a circuit foresees that the current generated by the voltage current converter
9
, in function of the input voltage Vin placed in input, is mirrored by the block
13
and stored in the capacitor C, when the signal In is low (therefore inverted signal In high and transistors
18
and
20
OFF and transistor
19
ON).
It is to be noted that the input voltage Vin and, therefore, the current generated by the converter
9
, follow the same variability of the pulse length causing that the generated current by the converter
9
can not be too little, penalty an increment of the mirror error of the block
13
. This happens because due to a mirror realized with MOS transistors working in depth inversion the mirror error is inversely proportional to the square of the used current.
Moreover the precision of a current having a very low value is limited by the presence of the leakage currents of the junctions making the various transistors.
Moreover the highest current can not be too high for consumption reasons.
Moreover, in order to obtain a correct way of working, the highest current can not be too high because the voltage drop on the transistors of the block
13
must not exceed a given value, elaborated in function of the supply voltage value Vcc and of the implementing parameters of the MOS transistors.
Moreover the dimensioning of the passive components of the circuit, that is of the resistance R and of the capacitor C, besides the dimensioning of the mirror
13
, have to be evaluated so as to maintain unchanged the performances of the circuit also in extreme conditions of working.
In fact the known circuits, if the variability of the input voltage Vin is higher, show a incorrect dimensioning of the components favoring therefore an inaccuracy for little input voltage, because this provides long pulses, and a high consumption for high voltages, because this provides short pulses.
In
FIG. 4
a schematic circuit, pointed with
43
, of the controlled voltage monostable circuit according to the present invention is shown.
In such a Figure there are noted a first block
21
, adapted to realize a voltage current converter, a second block
22
adapted to realize a storing circuit, a third block
23
adapted to realized a comparator, and a fourth block
24
adapted to realized a control logic.
The block
21
has a voltage current converter
25
connected to a supply line Vin, to a first switch
26
and to the block
23
.
The switch
26
is controlled to switch by a line In between a state connected to ground and a state connected to the block
22
.
The block
22
has a comparator
27
having its own non inverting terminal connected to said first switch
26
, to a second switch
28
and to the block
29
.
The comparator
27
having its own inverting terminal connected to a reference voltage Vref and its own output terminal connected with an output line Out. The switch
28
is controlled to switch, between a state connected to ground and an open circuit state, by the inverted version of the signal In, that is by the inverted In.
The block
23
is realized by a couple of comparators
30
and
31
having their own non inverting terminals connected with said voltage current converter
25
and their own outputs with said control logic
24
.
The comparator
30
has its own non inverting terminal connected with a first reference current Imax, while the comparator
31
has its own non inverting terminal connected with a second reference current Imin.
The control logic
24
has a first input
32
connected with the output terminal of said second comparator
30
, a second input terminal
33
with the output terminal of said comparator
31
, a third input terminal
34
with a timing signal Clk and an output terminal
35
connected with said voltage current converter
25
and with said block
29
.
Particularly the voltage current converter
25
, thanks to a resistive block, hereinafter shown in
FIG. 5
, has a transconductance that can assume N distinct resistive values each other scaled correspondently to the assumed value by the control digital value on the output terminal
35
of the logic
24
, that is:
g
m
=R, R/K, R/K
2
, . . . , R/K
N
where K is number greater than one.
Particularly the block
29
is realized by an array of N capacitors C, each of them is K time smaller than the previous, that is:
C, C/K, C/K
2
, . . . , C/K
N
Particularly the first value of the reference current Imax of the comparator
30
is connected with the second value of the reference current Imin by the following relationship:
Imax=A*Imin
Particularly the block
24
realizes an up/down counter that receives the timing signal Clk from an external timing generator (not shown in Figure) and the digital output
35
of which controls the transconductance g
m
of the voltage current converter
25
and it selects one of the capacitors of the array
29
.
In
FIG. 5
the circuit scheme of
FIG. 4
is shown in greater detail.
In fact the block
21
besides comprising the voltage current converter
25
and the switch block
26
comprises also a block
36
connected to the supply line Vcc.
Particularly the voltage current converter
25
is realized by a sense amplifier
37
, on the output of which is connected a n channel MOS transistor Mn
1
in source follower configuration and a resistive block
38
, connected by a side to the non inverting terminal of said sense amplifier
37
and to the source terminal of said transistor Mn
1
, and to the other side to the ground and it is controlled by the output
35
of the logic
24
.
The block
36
is realized by a couple of p channel MOS transistors Mp
1
and Mp
2
placed in mirror configuration, wherein the transistor in transdiode configuration Mp
1
is connected to the drain terminal of said transistor Mn
1
and the transistor Mp
2
is connected to the switch block
26
.
The switch block
26
is realized by a further couple of p channel MOS transistors
39
and
40
, wherein the first transistor
39
has the gate terminal connected to the signal In, the source terminal connected to ground and the drain terminal in common with the drain terminal of the second transistor
40
.
Said second transistor
40
has the gate terminal connected to the inverted signal In whilst the source terminal is connected to the block
22
.
The switch
28
is realized by an n channel MOS transistor
41
having the gate terminal connected to the inverted signal In, the drain terminal connected with the non inverting terminal of said comparator
27
and with the transistor
40
, and the source terminal connected to ground.
The comparator block
23
has two comparators
30
and
31
that are implemented using two p channel MOS transistors Mp
3
and Mp
4
added to the current mirror
36
and having two n channel MOS transistors Mn
3
and Mn
3
respectively as reference current generators Imax and Imin, being the transistors Mn
2
and Mn
3
biased by a reference current generator Iref by means of a further n channel MOS transistor
42
, having its own gate terminal connected to the gate terminals of said transistors Mn
2
and Mn
3
and its own source terminal connected to the source terminals of said transistors Mn
2
and Mn
3
.
The drain terminal of the transistor Mp
4
is connected to the input terminal
32
of the block
24
and the drain terminal of the transistor Mp
3
is connected to the input terminal
33
of the block
24
.
Particularly the terminal
32
is the detecting of a high signal (UP) and the terminal
33
is the detecting of a low signal (DOWN).
The way of working of such a circuit foresees the generation of a current from the voltage current converter
25
in function of the input voltage and by feedback from the digital output
35
.
Said current is mirrored by the block
36
and stored in a capacitor of the block
29
in function of said digital output
35
, when the signal In is low.
Particularly in the inventive embodiment the couple resistance
38
, adapted to determine the transconductance g
m
of the voltage current converter
25
, and the capacitor
29
, is, therefore, chosen by the logic
24
so as to maintain the generated current in the value range between Imin and Imax. All the N couples of resistances
38
and capacitors
29
have the same resistance for capacitor product value.
A possible embodiment foresees that for every resistance capacitor couple there is a respective switch (not shown in Figure) controlled in function of the digital word contained in the output
35
of the block
24
, so as to select a resistance able to maintain the current generated by the converter
25
in the value range between Imin and Imax.
The couple of inputs
32
and
33
of the logic
24
, that is the outputs of the comparators
30
and
31
provide to the logic block
24
the news of increment, in the case of the current generated by the converter
25
is too high, and of decrement, in the case of the current generated by the converter
25
is too low, or no counting if the current generated by the converter
25
is in the comparison range Imin and Imax.
Particularly it is to be noted that the news of increment means inserting a resistance
38
immediately higher, and it vales the dual for the news of decrement.
Therefore the logic
24
is a correction circuit of the signal generated by the voltage current converter
25
.
By way of example thinking that the input voltage Vin is incrementing, the resistance commutations happen as described by the following table:
|
Vin min
Vin max
Cor min
Cor. max
Res.
Cap.
|
|
R Imin
R Imax
Imin =
Imax
R
C
|
Imax/A
|
K R Imax
K R Imax
Imax/K
Imax
K R
C/K
|
. . .
. . .
. . .
Imax
. . .
. . .
|
K
N-2
R Imin
K
N-1
R Imax
Imax/K
Imax
K
N-1
R
C/K
N-1
|
|
K must be less or equal to A, because the inserting of one of the N resistances of the resistive block
38
is that one immediately higher so as to re-enter the current generated by the converter
25
in the range between Imin and Imax.
The ratio between the maximum and minimum input voltage, that is (Vin max/Vin min), among which the current remains contained in the range between Imin and Imax, is: K
N−1
*A.
If K=A is chosen, the ratio (Vin max/Vin min) is the highest, whilst if K<A, the obtainable range by the ratio (Vin max/Vin min) is reduced, but an hysteresis useful to make stronger the circuit with respect to eventual noises on the outputs of the two comparators
30
and
31
is introduced.
It is to be noted also that if the input voltage is incrementing the plurality of resistances
38
are switched so as the current generated by the converter
25
remains always around the highest values of the range Imin and Imax, that is between Imax/K and Imax.
In the case of the input voltage is decrementing, the current generated by the converter
25
remains always around the lowest values of the range Imin and Imax, that is between Imim and K*Imim.
In
FIG. 6
an application of the controlled voltage monostable circuit according to the present invention is shown.
In such a figure it is to be noted the inventive circuit
43
is connected with a logic block
48
and with a first divider block
46
.
The logic block
48
is connected to a comparator
47
and to a power output stage
45
.
The power block
45
is connected with a supply line Vin′ and it outputs a voltage Vout′.
The block
46
is a divider having a prefixed damped ratio Δ. Said block receives in input the input voltage Vin′ and outputs the control voltage if the inventive circuit
43
, that is Vin.
The block
45
is realized by a power MOS stage HS and LS, wherein the transistor Hs has the drain terminal connected to the supply line Vin′, the gate terminal with the block
48
and the source terminal in common with the drain terminal of the transistor LS and with a load L′-C′.
The transistor LS has the source terminal connected to ground and the gate terminal connected with said block
48
.
The application shown in
FIG. 6
is a dc-dc buck converter, that is a converter wherein Vout′ is lower than Vin′. Particularly the monostable circuit
43
determines the length of the turning on of the MOS HS that connects to the input line the inductor L′.
The instant of turning on is elaborated by the comparator
47
that compares the current that flows in the inductor L′, the voltage on the capacitor C′ with a reference voltage Vref′, so as to turn on said MOS HS when the linear combination of the current that flows in the inductor L′ and of the voltage on the capacitor C′ decreases under a reference value Vref.
Being the switching period directly proportional to the length of the pulse, to the input voltage Vin′ and inversely proportional to the output voltage Vout′, by using the inventive monostable circuit
43
it is obtainable that the switching frequency of the same monostable
43
is independent from the input voltage Vin′.
In fact the length of the pulse can be written as:
t
ON
=Ω/Vin′
(1)
where Ω is the constant of the monostable
43
.
The switching frequency is:
f
SW
=Vout
′/(
Vin′*t
ON
) (2)
Therefore the input voltage Vin of the monostable
43
is:
Vin=Δ*Vin′=Ω*f
SW
*Vin′/Vout′
(3)
It is possible to deduce that the variation of Vin is the sum of the variations of Vin′ and f
SW
.
Claims
- 1. A monostable circuit for providing a delay that is inversely proportional to an input signal, comprising:means for generating a signal proportional to an input signal and to a corrective factor; means for comparing the value of said generated signal with a prefixed value range; and means for correcting said corrective factor if the value of said generated signal is out of said prefixed value range.
- 2. A monostable circuit according to claim 1, in which said generating means comprises a voltage-to-current converter connected on one side to a comparator and to a capacitive block, including a plurality of capacitors, by means of a switch block, and, on the other side, with said comparing means.
- 3. A monostable circuit according to claim 2, in which said voltage-to-current converter comprises a sense amplifier having an output terminal coupled to a first transistor in source follower configuration including a resistive block including a plurality of resistance values.
- 4. A monostable circuit according to claim 3 in which the first transistor comprises an N-channel MOS transistor.
- 5. A monostable circuit according to claim 3, in which said resistive block comprises N different resistive values scaled to each other corresponding to the value of said corrective factor present on an output of said correction means.
- 6. A monostable circuit according to claim 2, in which said capacitive block comprises a plurality of capacitor values.
- 7. A monostable circuit according to claim 1, in which said comparing means comprises a comparator.
- 8. A monostable circuit according claim 7, in which said comparator comprises second and third transistors coupled respectively to fourth and fifth transistors.
- 9. A monostable circuit according to claim 8 in which the second and third transistors each comprise an N-channel MOS transistor.
- 10. A monostable circuit according to claim 8 in which the fourth and fifth transistors each comprise an N-channel MOS transistor.
- 11. A monostable circuit according to claim 7, further comprising a sixth transistor for biasing said fourth and fifth transistors.
- 12. A monostable circuit according to claim 11 in which the sixth transistor comprises an N-channel MOS transistor.
- 13. A monostable circuit according to claim 6, in which said correction means comprises an input coupled to the outputs of said second and third MOS transistors and an output for providing said corrective factor in order to maintain said value of said generated signal in the value range of said comparing means.
- 14. A monostable circuit according to claim 8, in which the product of said resistance value and said capacitor value is constant.
- 15. A method for generating a delay having a length inversely proportional to signal, comprising:a) generating a signal proportionally to an input signal and to a corrective factor; b) comparing the value of said generated signal with a prefixed value range; and c) correcting said corrective factor in the case that said generated signal is out of said prefixed value range.
- 16. A DC-to-DC buck converter circuit comprising:a divider having an input for receiving an input signal and an output; a monostable circuit for providing a delay inversely proportional to and having a switching frequency independent of said input signal, having an input coupled to the output of the divider, and an output; a logic block having an input coupled to the output of the monostable circuit, and an output; a power block having an input coupled to the output of the logic block, and an output for providing an output voltage; and a comparator in communication with said power block for providing feedback to said logic block.
Priority Claims (1)
Number |
Date |
Country |
Kind |
MI2001A0057 |
Jan 2001 |
IT |
|
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Number |
Name |
Date |
Kind |
4039868 |
Aono et al. |
Aug 1977 |
A |
5506533 |
Wu |
Apr 1996 |
A |
6498617 |
Ishida et al. |
Dec 2002 |
B1 |