1. A MEMS element comprising:
a substrate;
a first electrode formed above the substrate; and
a second electrode having a support portion and a beam portion, the support portion being formed above the substrate, the beam portion extending from the support portion, being formed in a state of having a gap between the first electrode and the beam portion, and being capable of vibrating in a thickness direction of the substrate, wherein
the width of the beam portion decreases with distance from a base of the beam portion toward a tip of the beam portion,
the central length of the beam portion is larger than the length of an end of the beam portion,
the width of the base of the beam portion is larger than the central length of the beam portion, and
the beam portion includes:
a first part having a rectangular shape in plan view and the central length of the beam portion, and
a second part adjacent to the first part and having the length of the end of the beam portion, wherein
the length of the second part decreases with distance from the first part.
2. The MEMS element according to claim 1, wherein
the second part has a trapezoidal shape in plan view.
3. An oscillator comprising:
the MEMS element according to claim 2, and
a circuit portion electrically connected with the first electrode and the second electrode of the MEMS element.
4. An oscillator comprising:
the MEMS element according to claim 1, and
a circuit portion electrically connected with the first electrode and the second electrode of the MEMS element.
5. A MEMS element comprising:
a substrate;
a first electrode formed above the substrate; and
a second electrode having a support portion and a beam portion, the support portion being formed above the substrate, the beam portion extending from the support portion, being formed in a state of having a gap between the first electrode and the beam portion, and being capable of vibrating in a thickness direction of the substrate, wherein
the width of the beam portion decreases with distance from a base of the beam portion toward a tip of the beam portion,
the central length of the beam portion is larger than the length of an end of the beam portion,
the width of the base of the beam portion is larger than the central length of the beam portion, and
the beam portion includes:
a first part having the central length of the beam portion, and
a second part adjacent to the first part and having the length of the end of the beam portion, wherein
the length of the second part decreases with distance from the first part, and
the beam portion has only one continuous arc or elliptical-arc shape in plan view.
6. An oscillator comprising:
the MEMS element according to claim 5, and
a circuit portion electrically connected with the first electrode and the second electrode of the MEMS element.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A power supply for supplying a current through series combination of an inductor and a transistor, comprising:
a control system adapted to control the current according to an inductor current signal; and
a current sensor connected to the control system, wherein the current sensor:
is adapted to generate an inductor current signal according to a sensed current in the inductor; and
comprises a series combination of a first resistor and a second resistor, wherein the series combination is adapted to be connected in parallel to the series combination of the inductor and the transistor.
2. A power supply according to claim 1, wherein a ratio of a resistance of the first resistor to a resistance of the second resistor substantially matches a ratio of a lead inductance of the transistor to an inductance of the inductor.
3. A power supply according to claim 1, wherein the current sensor further comprises a third resistor comprising a first terminal adapted to be connected to a terminal of the transistor and a second terminal connected to the control system, wherein a resistance of the third resistor is selected according to a selected range of inductor current signal values to represent a selected range of sensed currents.
4. A power Supply according to claim 1, further comprising a differential amplifier comprising:
a first input adapted to be connected to a node between the inductor and the transistor;
a second input connected to a node between the first resistor and the second resistor.
5. A power supply according to claim 4, wherein the current sensor further comprises a third resistor, wherein:
the first input of the amplifier is adapted to be connected to the node between the inductor and the transistor via the third resistor; and
a resistance of the third resistor is selected according to a scaled range of output signals corresponding to a selected range of sensed current.
6. A power supply according to claim 4, further comprising a second transistor having a first terminal connected to an output of the amplifier, wherein the second transistor is adapted to generate the inductor current signal according to a signal from the amplifier.
7. A power supply according to claim 1, wherein the control system comprises a PWM controller.
8. A power supply according to claim 1, wherein a voltage VP at a node between the first resistor and the second resistor is configured to be:
V
P
=
R
L
\ue89e
\ue89e
1
R
L
\ue89e
\ue89e
1
+
R
L
\ue89e
\ue89e
2
\xd7
V
out
where RL1 is a resistance of the first resistor, RL2 is a resistance of the second resistor, and Vout is an output voltage of the series combination of the inductor and the transistor.
9. A power supply according to claim 1, wherein a voltage VN at a node between the inductor and the transistor is configured to be:
V
N
=
L
lead
L
lead
+
L
buck
\xd7
V
out
–
R
FET
\xd7
I
out
where Llead is a lead inductance of the transistor, Lbuck is an inductance of the inductor, RFET is a resistance of the transistor, Iout is the current, and Vout is an output voltage of the series combination of the inductor and the transistor.
10. A power supply according to claim 1, wherein the inductor current signal is proportional to the sensed current independent of an absolute value of the inductor and an absolute value of a lead inductance of the transistor.
11. A power supply according to claim 1, wherein the inductor current signal is proportional to the sensed current independent of a regulated output voltage of the power supply.
12. A current sensor for providing an inductor current signal corresponding to a sensed current in a series combination of an inductor and a synchronous MOSFET during an ON state of the MOSFET, comprising:
a first resistor comprising a first terminal connected to a source terminal of the MOSFET;
a second resistor having a first terminal connected to a second terminal of the first resistor and a second terminal connected to the inductor; and
a differential amplifier comprising:
a first input connected to a node between the first resistor and the second resistor; and
a second input adapted to be connected to a drain terminal of the MOSFET.
13. A current sensor according to claim 12, wherein a ratio of a resistance of the first resistor to a resistance of the second resistor substantially matches a ratio of a lead inductance associated with the MOSFET to an inductance of the inductor.
14. A current sensor according to claim 12, wherein the current sensor further comprises a third resistor comprising a first terminal adapted to be connected to the drain terminal of the MOSFET, wherein a resistance of the third resistor is selected according to a selected range of inductor current signal values to represent a selected range of sensed currents.
15. A current sensor according to claim 12, wherein the current sensor further comprises a third resistor, wherein:
the first input of the amplifier is adapted to be connected to the drain terminal of the MOSFET via the third resistor; and
a resistance of the third resistor is selected according to a scaled range of output signals corresponding to a selected range of sensed current.
16. A current sensor according to claim 15, further comprising a transistor having a control terminal connected to an output of the amplifier, wherein the transistor is adapted to generate the inductor current signal according to a signal from the amplifier.
17. A current sensor according to claim 12, wherein a voltage VP at the node between the first resistor and the second resistor is configured to be:
V
P
=
R
L
\ue89e
\ue89e
1
R
L
\ue89e
\ue89e
1
+
R
L
\ue89e
\ue89e
2
\xd7
V
out
where RL1 is a resistance of the first resistor, RL2 is a resistance of the second resistor, and Vout is an output voltage of the series combination of the inductor and the MOSFET.
18. A current sensor according to claim 12, wherein a voltage VN at the drain terminal of the MOSFET is configured to be:
V
N
=
L
lead
L
lead
+
L
buck
\xd7
V
out
–
R
FET
\xd7
I
out
where Llead is a lead inductance of the MOSFET, Lbuck is an inductance of the inductor, RFET is a resistance of the MOSFET, Iout is the sensed current, and Vout is an output voltage of the series combination of the inductor and the MOSFET.
19. A current sensor according to claim 12, wherein the inductor current signal is proportional to the sensed current independent of an absolute value of the inductor and an absolute value of a lead inductance of the MOSFET.
20. A method of generating an inductor current signal corresponding to a current in a series combination of an inductor and a transistor, comprising:
connecting a series combination of a first resistor and a second resistor in parallel with the series combination of the inductor and the transistor; and
selecting resistance values for the first resistor and the second resistor according to a lead inductance associated with the transistor and an inductance of the inductor, wherein a ratio of a resistance of the first resistor to a resistance of the second resistor substantially matches a ratio of the lead inductance of the transistor to the inductance of the inductor.
21. A method of generating an inductor current signal according to claim 20, further comprising:
receiving a first signal at an amplifier from a node between the first resistor and the second resistor;
receiving a second signal at the amplifier from a node between the inductor and the transistor; and
generating the inductor current signal according to a difference between the first signal and the second signal.