What is claimed is:
1. A control unit for an electric power steering apparatus that controls a motor for giving steering assist force to a steering mechanism based on a current control value calculated from a steering assist command value calculated by calculating means based on the steering torque generated in the steering shaft, and a current value of the motor, the control unit for an electric power steering apparatus comprising a steering wheel return controller for applying a steering wheel return control signal to the steering assist command value, thereby to execute the steering wheel return control only when the steering wheel returns.
2. A control unit for an electric power steering apparatus according to claim 1, wherein the steering wheel return controller comprises: a steering wheel return basic current circuit that inputs a steering angle and outputs a steering wheel return basic current value; a gain circuit that inputs a vehicle speed and outputs a gain of a predetermined function; a sign decision circuit that inputs the steering angle and a steering angular velocity and decides whether the signs of these inputs coincide with each other or not; a multiplier that multiplies the steering wheel return basic current value with the gain; and a switching section that switches an output of the multiplier based on an output of the sign decision circuit.
3. A control unit for an electric power steering apparatus according to claim 2, wherein the switching section switches between a case where an output of the multiplier is outputted straight and a case where a zero is outputted.
4. A control unit for an electric power steering apparatus according to claim 2, the control unit comprising a steering angle sensor that detects the steering angle, and detects an absolute angle of the steering wheel.
5. A control unit for an electric power steering apparatus that controls a motor for giving steering assist force to a steering mechanism, and controls the steering wheel to a neutral point by using a steering angle sensor, based on a current control value calculated from a steering assist command value calculated by calculating means based on the steering torque generated in the steering shaft, and a current value of the motor, the control unit for an electric power steering apparatus comprising a steering wheel return controller for applying a steering wheel return control signal to the steering assist command value, thereby to always execute the steering wheel return control and the astringency control.
6. A control unit for an electric power steering apparatus according to claim 5, the control unit comprising a vehicle speed sensor, wherein the steering wheel return controller inputs a vehicle speed from the vehicle speed sensor and a steering angle from the steering angle sensor, and also inputs a steering angular velocity.
7. A control unit for an electric power steering apparatus according to claim 6, wherein the control unit converts the steering angle into a steering wheel return basic current value, converts the vehicle speed into a vehicle speed response gain, converts the steering angular velocity into a steering angular velocity response gain, and uses a multiplied value of the steering wheel return basic current value, the vehicle speed response gain, and the steering angular velocity response gain, as the steering wheel return control signal.
8. A control unit for an electric power steering apparatus according to claim 5, wherein the steering wheel return controller comprises: a steering wheel return basic current circuit that inputs a steering angle and outputs a steering wheel return basic current; a first gain circuit that inputs a vehicle speed and outputs a gain based on a first function; a second gain circuit that inputs a steering angular velocity and outputs a gain according to a second function; a first multiplier that multiplies the steering wheel return basic current with the gain according to the first function; and a second multiplier that multiplies an output of the first multiplier with the gain according to the second function.
9. A control unit for an electric power steering apparatus according to claim 8, the control unit comprising a steering angle sensor that detects the steering angle, and detects an absolute angle of the steering wheel.
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 multi-state current-switching magnetic memory element configured to store a state by current flowing therethrough to switch the state comprising:
a stack of two or more magnetic tunneling junctions (MTJs), each MTJ having a free layer with a switchable magnetic orientation, a barrier layer and a fixed layer, each MTJ of the stack being separated from other MTJs in the stack by at least one amorphous isolation layer, the stack operable to store more than one bit of information with each MTJ storing one bit of information, each of the free layers having a different composition based on the amount of oxide therein, and each of the free layers of the stack being responsive to a unique switching current based on the composition of the free layer,
wherein the free layer switches its magnetic orientation based upon the level of the switching current applied thereto, wherein different levels of current applied to the memory element causes switching to different states.
2. A multi-state current-switching magnetic memory element, as recited in claim 1, wherein each of the MTJs of the stack has a distinct size.
3. A multi-state current-switching magnetic memory element, as recited in claim 1, wherein the free layers of the MTJs each have a unique thickness, thereby causing each MTJ to switch states at a unique switching current.
4. A multi-state current-switching magnetic memory element, as recited in claim 1, wherein the barrier layers of the MTJs each have a unique thickness, thereby causing each MTJ to switch states at a unique switching current.
5. A multi-state current-switching magnetic memory element, as recited in claim 4, wherein the barrier layer of each of the MTJs is made substantially of magnesium oxide (MgO) and may include one or more of the following compounds\u2014aluminum oxide (Al2O3), titanium oxide (TiO2), magnesium oxide (MgOx), ruthenium oxide (RuO), strontium oxide (SrO), Zinc oxide (ZnO).
6. A multi-state current-switching magnetic memory element, as recited in claim 5, wherein each of the MTJs includes a fixed layer, and a barrier layer, the barrier layer separating the fixed layer and the free layer.
7. A multi-state current-switching magnetic memory element, as recited in claim 6, wherein the fixed layer of each of the MTJs is made substantially of magnetic material.
8. A multi-state current-switching magnetic memory element, as recited in claim 7, further including a pinning layer formed adjacent to the fixed layer of each of the MTJs.
9. A multi-state current-switching magnetic memory element, as recited in claim 8, further including a bottom electrode on top of which is formed the pinning layer of one of the MTJs.
10. A multi-state current-switching magnetic memory element, as recited in claim 9, further including a top electrode formed on top of the free layer of one of the MTJs.
11. A multi-state current-switching magnetic memory element configured to store a state by current flowing therethrough to switch the state comprising:
a first magnetic tunneling junction (MTJ) formed on top of a bottom electrode;
a second MTJ, formed on top of the first MTJ, and the second MTJ separated from the first MTJ by and an amorphous isolation layer; and
a top electrode formed on top of the second MTJ, each of the first and second MTJ having a free layer with a switchable magnetic orientation, a barrier layer and a fixed layer, the first and second MTJs collectively operable to store more than one bit of information with each of the first and second MTJs storing one bit of information, each of the free layers of the first and second MTJs having a different composition based on the amount of oxide therein, and each of the free layers of the first and second MTJs being responsive to a unique switching current based on the composition of the free layer,
wherein the free layer switches its magnetic orientation based upon the level of the switching current applied thereto, wherein different levels of current applied to the memory element causes switching to different states.
12. A multi-state current-switching magnetic memory element, as recited in claim 11, further including a first pinning layer formed between the bottom electrode and the first MTJ.
13. A multi-state current-switching magnetic memory element, as recited in claim 12, further including a second pinning layer formed between the seeding layer formed on top of the insulation layer, and the second MTJ.
14. A multi-state current-switching magnetic memory element, as recited in claim 13, wherein each MTJ includes a fixed layer, and a barrier layer, the barrier layer separating the free layer from the fixed layer.
15. A multi-state current-switching magnetic memory element, as recited in claim 14, wherein the barrier layer of each MTJ is made substantially of magnesium oxide (MgO) and may include one or more of the following compounds\u2014aluminum oxide (Al2O3), titanium oxide (TiO2), magnesium oxide (MgOx), ruthenium oxide (RuO), strontium oxide (SrO), Zinc oxide (ZnO).
16. A multi-state current-switching magnetic memory element, as recited in claim 15, wherein the barrier layer of each MTJ has a unique thickness, thereby causing each MTJ to have a unique resistance.
17. A multi-state current-switching magnetic memory element, as recited in claim 16, wherein the fixed layer of each of the MTJs is made substantially of magnetic material.
18. A multi-state current-switching magnetic memory element, as recited in claim 17, wherein the free layer of each of the MTJs is unique in composition, causing each MTJ to have a unique switching current.
19. A multi-state current-switching magnetic memory element, as recited in claim 11, wherein each of the first and second MTJs has a distinct size.
20. A programerase circuit comprising:
a first current source;
a second current mirror circuit coupled to the current source;
a first switch;
a second switch coupled to the first switch;
a multi-state current-switching magnetic memory cell coupled to the second switch, the multi-state current-switching magnetic memory cell including a plurality of magnetic tunnel junction (MTJs), the MTJs being separated from each other by at least one amorphous isolation layer, at least two of the MJTs having free layers with different compositions based on the amount of oxide therein, and each of the free layers of the at least two MTJs being responsive to a unique switching current based on the composition of the free layer,
wherein the free layer switches its magnetic orientation based upon the level of the switching current applied thereto, wherein different levels of switching current applied to the memory element causes the at least two MTJs to switch to different states;
a third switch coupled to the multi-state current-switching magnetic memory cell;
a second current source; and
a second current mirror circuit coupled to the second current source and to the first switch,
wherein the MTJs are programmed by applying a first current level to the first current source and a second current level to the second current source to cause varying current levels through the MTJs, the first and second current levels being different from one another and wherein switching the first, second, and third switches causes selectively to program or erase the MTJs of the multi-state current-switching magnetic memory cell.
21. A programerase circuit, as recited in claim 20, wherein the multi-state current-switching magnetic memory cell further includes an access transistor coupled to one of the MTJs of the multi-state current-switching magnetic memory cell.
22. A programerase circuit, as recited in claim 20, wherein the MTJs of the multi-state current-switching magnetic memory cell are coupled to each other.
23. A read circuit comprising:
a memory cell including a first and a second magnetic tunnel junction (MTJ), each of the first and second MTJs having a resistance associated therewith, the first and second MTJs being separated from each other by at least one amorphous isolation layer, the first and second MTJ each having a free layer and the free layers of the first and second MTJs having different compositions based on the amount of oxide therein, and each of the free layers of the first and second MTJs being responsive to a unique switching current based on the composition of the free layer;
a sense amplifier coupled to the memory cell;
a reference circuit coupled to the sense amplifier, the reference circuit including a plurality of state reference circuits, each of the plurality of state reference circuits having a resistance associated therewith,
wherein the first and second MTJs are read using the sense amplifier by comparing the resistances of the first and second MTJs to the resistances of the plurality of state reference circuits.
24. A read circuit, as recited in claim 23, wherein the memory cell includes an access transistor operable to select one of the first and second MTJs for reading.
25. A read circuit, as recited in claim 23, wherein the reference circuit includes a plurality of access transistors for selecting a state reference circuit for reading the first or second MTJs.