This application claims priority to Swedish application no. 0302107-8 filed Jul. 18, 2003.
The present invention generally relates to the field of integrated circuit technology, and more specifically the invention relates to a monolithically integrated electromagnetic device, and to a method of operating such an electromagnetic device.
Integrated inductors have found widespread use in integrated circuits for RF (radio frequency) applications. They occupy quite much space, where typically no other circuit elements can be located.
Integrated RF circuits are usually implemented with RLC type of elements in a design style that has been inherited from solutions with discrete devices on printed circuit boards. The main difference is that integrated circuit devices have some quite different data, especially concerning figures-of-merit and cross-couplings.
Integrated inductors have been difficult to design due to lack of simulation tools and understanding of electromagnetic interaction with the substrate. Therefore, the inductors have been localized in areas separated from devices to avoid interference. However, such design may result in bulky and thus slow devices.
It is an object of the present invention to provide an electromagnetic device in an integrated circuit, particularly an integrated circuit for radio frequency applications, which overcomes the problems associated with the prior art.
It is thus a particular object of the invention to provide such an electromagnetic device, by which new design rules for integrated circuits can be employed, which will result in area and possibly speed loss of the devices fabricated.
It is a further object of the invention to provide a method of operating such an electromagnetic device.
These objects can be attained, according to the present invention, by an electromagnetic device in an integrated circuit, particularly an integrated circuit for radio frequency applications, comprising an MOS transistor structure and a spiral inductor, wherein the MOS transistor structure and the spiral inductor are arranged on top of each other to obtain an operative coupling between a MOS current of the MOS transistor structure and a magnetic field of the spiral inductor via the Hall effect, and an electric input is provided for controlling an electric quantity of a first one of the MOS transistor structure and the spiral inductor in order to influence the operation of the second one of the MOS transistor structure and the spiral inductor via the operative coupling.
The electric input can be provided for controlling an electric quantity of the MOS transistor structure in order to influence the operation of the spiral inductor via the operative coupling. The electric quantity can be a gate voltage of the MOS transistor structure. The electric input can be provided for influencing the Q value of the spiral inductor via the operative coupling. The electric input can be provided for influencing the inductance of the spiral inductor via the operative coupling. The electric input can be provided for controlling an electric quantity of the spiral inductor in order to influence the operation of the MOS transistor structure via the operative coupling. The electric quantity can be a current in the spiral inductor. The electric input can be provided for influencing a MOS current of the MOS transistor structure. The MOS transistor structure may comprise a split drain structure including two separated drains, and the electric input can be provided for influencing a differential current through the two separated drains. The electromagnetic device can be provided for operating as an amplifier having a current in the spiral inductor as input and the differential current through the two separated drains as output.
The objects can also be attained by a method of operating an integrated circuit based electromagnetic device comprising an MOS transistor structure and a spiral inductor, comprising the steps of:
The method may further comprise the step of controlling an electric quantity of the MOS transistor structure in order to influence the operation of the spiral inductor via the operative coupling. The method may further comprise the step of influencing a Q value of the spiral inductor via the operative coupling. The method may further comprise the step of influencing the inductance of the spiral inductor via the operative coupling. The method may further comprise the step of controlling an electric quantity of the spiral inductor in order to influence the operation of the MOS transistor structure via the operative coupling. The method may further comprise the step of influencing an MOS current of the MOS transistor structure.
By providing a MOS transistor structure and a spiral inductor on top of each other to obtain an operative coupling between a MOS current of the MOS transistor structure and a magnetic field of the spiral inductor via the Hall effect, and by controlling an electric quantity of a first one of the MOS transistor structure and the spiral inductor in order to influence the operation of the second one of the MOS transistor structure and the spiral inductor via the operative coupling, an electromagnetic device is achieved, which occupies less space and by use of which faster integrated circuits can be fabricated.
In case of controlling an electric quantity of the MOS transistor structure in order to influence the operation of the spiral inductor, the electric quantity is advantageously a gate voltage of the MOS transistor structure, by which the Q value or the inductance of the spiral inductor can be controlled.
In case of controlling an electric quantity of the spiral inductor in order to influence the operation of the MOS transistor structure, the electric quantity is advantageously the current flown in the spiral inductor, or the magnetic field created by the spiral inductor, by which a MOS current of the MOS transistor structure can be controlled.
The electromagnetic device of the present invention can be used in a variety of devices such as e.g. inductors, amplifiers, VCO's, mixers, and modulators.
Further characteristics of the invention and advantages thereof will be evident from the detailed description of preferred embodiments of the present invention given hereinafter and the accompanying
In
By this arrangement an operative electromagnetic coupling between the two devices is obtained. A current 15a fed to an input 15 of the spiral inductor 12 is flown through the spiral inductor 12, and gives rise to a magnetic field 16, whose field lines penetrates through the MOS structure 11 and its gate 14.
Assuming a skin depth large enough, a circular current 17 similar to the current in the spiral inductor 12 but with opposite direction will be induced in the MOS transistor structure. The electrons are generated from the thermal Shockley-Read-Hall process provided that no source or drain exists. When the voltage of the gate 14 is increased, the surface is inverted and the circular current will increase. A result of this is that the spiral inductor 12 obtains higher losses, that is a higher Q-value.
The magnetic field 16 is thus operatively coupled to the MOS current 17 of the MOS structure 11 via the Hall effect. Generally, by controlling an electric quantity of the MOS transistor structure, e.g. the gate voltage, the operation of the spiral inductor, e.g. its Q value or its inductance, can be influenced and controlled via the operative Hall effect coupling.
In
By feeding a current 15a to the input 15 of the spiral inductor 12 and flowing this current through the spiral inductor 12 a magnetic field 16 is created above and within the MOS transistor structure 11′. A MOS current from the source 21 to the split drain structure 22a-b will be deflected due to the Hall effect towards one of the drains 22a, 22b depending on the direction of the magnetic field. This is schematically indicated by the two arrows 23a, 23b.
It is important to have an appropriate coupling strength between the magnetic field 16 and the induced MOS current 17. Sensitivities of about 1 V/T have been reported for CMOS based Hall effect sensors.
From the basic theory of electromagnetism one has
B=φ/A, (1)
where B is the magnetic flux density [Vs/m2], φ is the magnetic flux, and A is the area. Further, Hds=N×I, (2)
where H is the magnetizing flux, N is the number of turns of the spiral inductor, and I is the current flown through the spiral inductor. Still further,
B=μ0H (3)
where μ0 is the permeability, i.e. about 4π10−7 Vs/A/m=1.2 10−6H/m, and
Φ=L×I, (4)
where L is the inductance of the spiral inductor.
For a wire having a radius a, the magnetic flux density is given by
Typical values for an integrated spiral inductor, I=100 mA, N=5 turns, a=10 microns, will give a magnetic field B of about 0.01 Tesla and about 10 mV between the two drains for the typical sensitivity of a Hall effect CMOS sensor.
Note that the magnetic flux density is proportional to the current and the number of turns as well as inversely proportional to the radius of the inductor. This means that a scaled electromagnetic RF device of the present invention follows the general scaling rules for VLSI. A major trend today is a reduction of feature sizes and an increase of the number of metal layers. This makes the invention even more relevant for future technologies.
The electromagnetic device of
The design of the split drain MOS transistor is illustrated in
Still further, a proper geometry will affect the linearity between differential output current and applied magnetic field. For variable Q and variable inductance devices, amplifiers, and mixers the linearity should be high. For mixers it should be high. For oscillators it depends on the application, but usually high linearity is desired.
In
The drain currents 11 and 12 are given by the following equations:
ID1=β(VG−VT)VD1F(I1−I2)) (6)
ID2=β(VG−VT)VD2F(I2−I1)) (7)
where VD1 and VD2 are drain voltages on the two respective drains 22a, 22b.
By using appropriate dimensions of the device of
The electromagnetic device of the present invention will offer a new coupling mechanism that might be very useful in RF-IC design. MOS circuits, which already contain inductors and transistors, have RF building blocks that require several connections to perform desired operations. Areas for inductors, previously unused for other purposes, will according to the invention contain transistors, by which higher packing density and thus smaller and faster circuits can be achieved. The characteristics of the new coupling mechanism between a magnetic flux of a spiral inductor and a MOS current of a MOS transistor structure can be employed in a large range of building blocks.
It shall be appreciated that while the present invention is primarily intended for silicon based RF integrated circuits, it may nevertheless be realized in other material systems such as e.g. GaAs and/or for other kind of applications.
Number | Date | Country | Kind |
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0302107-8 | Jul 2003 | SE | national |