Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2001-12-10
2003-12-09
Mis, David C. (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S10800D, C331S1170FE, C331S17700V, C331S179000
Reexamination Certificate
active
06661301
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to an oscillator circuit.
Voltage-controlled oscillators (VCO) are used, for example in transmitting and receiving systems in particular in RF radiofrequency (high frequency) technology. By way of example, voltage-controlled oscillators can be used for constructing phase-locked loops (PLL). In that case, there may be the requirement, on the one hand, that the oscillation frequency of the oscillator be adjusted in an analog manner, that is in an infinitely variably manner. Furthermore, it may also be desired, however, that the oscillation frequency of the oscillator be changed over in discrete steps.
In integrated voltage-controlled oscillators, LC resonant circuits are usually used as the resonator. Those circuits are based on the principle that an LC resonator is deattenuated by means of an amplifier. See, for example, Tietze and Schenk,
Halbleiter
-
Schaltungstechnik
[Semiconductor circuitry], 10
th
ed. 1993, p. 458 et seq. In that case, the oscillation frequency of the LC oscillator results from the effective inductance and the effective capacitance of the oscillator circuit.
The continuously variable adjustment of the frequency of an LC oscillator is usually effected by way of variable-capacitance diodes which are operated in the reverse direction and whose capacitance value depends on the applied reverse voltage. By contrast, the process of altering the oscillation frequency in fixed discrete steps can be effected by activating or deactivating capacitances with a fixed capacitance value.
If capacitances are connected into an LC resonant circuit, then the resonant circuit frequency is detuned toward lower frequencies. If the switches are open, however, only the parasitic capacitances of the switchable capacitor and of the switch itself act as frequency-detuning elements.
German patent application DE 43 32 798 A1 describes a circuit configuration for a tunable resonant circuit wherein, in the resonator, a respective switch is connected in series with a respective capacitance. The capacitance values are graduated in a binary manner. The resonant frequency of the oscillator can thus be changed over between a plurality of steps.
The published document by Darabi and Abidi,
A
4.5-
mW
900-
MHz CMOS Receiver For Wireless Paging,
IEEE Journal of Solid-State Circuits, Vol. 35, No. 8, 2000, pages 1085-1095, specifies an adjustable filter whose filter properties can be changed over by binary-graduated capacitances which are connected in parallel being connected or disconnected by means of a respective CMOS switching transistor arranged in series with a respective capacitance.
The published document by Mourant, et al.,
A Low Phase Noise Monolithic VCO in SiGe BiCMOS,
IEEE 2000 No. 0-7803-5687-X/00 specifies in
FIG. 2
a VCO circuit diagram having both tuneable variable-capacitance diodes D
3
, D
4
and changeover switches, which in each case comprise two transistors using MOS technology.
The published document Kral, et al.,
RF
-
CMOS Oscillators with Switched Tuning,
IEEE 1998, Custom Integrated Circuits Conference, 1998, pages 555-58, shows a voltage-controlled LC oscillator wherein capacitances are provided for the range changeover. A respective radio frequency switch is assigned to and connected in series with the capacitances.
The oscillator circuits specified in the above prior art have in common the disadvantage that they have either a comparatively large parasitic capacitance of the switch in the switched-off state and/or a comparatively large series resistance of the switch in the switched-on state. This is due to the fact that when MOS transistors are used as electronic switches, a large transistor is required in order to obtain a small on-series resistance, but a small transistor is required in order to obtain small parasitic capacitances in the switched-off state.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an oscillator circuit, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and wherein the oscillation frequency of the oscillator is embodied such that it can be changed over. At the same time, the intention is for parasitic capacitance and on-state resistance of the changeover switches to be low in order to obtain a large capacitance ratio between different switching states and also good phase noise properties.
With the foregoing and other objects in view there is provided, in accordance with the invention, an oscillator circuit, comprising:
a symmetrically constructed oscillator core with a least one inductance and at least one capacitance forming a resonant circuit with a symmetrical oscillation node;
two switchable capacitances connected via a respective terminal to said oscillation node and forming a switching node at free terminals thereof; and
a switching unit connected to said switchable capacitances for altering a resonant circuit frequency by activating said switchable capacitances, said switching unit including a first switch for a direct low-impedance connection to one another of said free terminals of said switchable capacitances and further switches for a low-impedance connection of said free terminals of said switchable capacitances to a supply voltage.
In other words, the objects of the invention are achieved with the oscillator circuit that has at least the following features:
a symmetrically constructed oscillator core with at least one inductance and at least one capacitance, which form a resonant circuit with a symmetrical oscillation node;
two switchable capacitances, which are connected by a respective terminal to the oscillation node and form a switching node at their free terminals; and
a switching unit for altering a resonant circuit frequency by activating the switchable capacitances. The switching unit includes a first switch for the direct low-impedance connection of the free terminals of the switchable capacitances to one another, and further switches for the low-impedance connection of the free terminals of the switchable capacitances through to a supply voltage terminal.
The terms switch and switching means are used interchangeably and should be understood as synonyms of each other.
The first switching means can directly connect the two switchable capacitances in the switched-on state. Consequently, in the switched-on state of the first switching means, i.e. while the switchable capacitances are effectively connected to the resonator, only the series resistance of this first transistor takes effect. In order to activate the switchable capacitances, a potential connection of the first switch to the supply voltage terminal is required in this case. This is achieved by the further switching means, which, with their controlled paths, connect the two terminals of the controlled path of the first switching means in the switched-on state to the supply voltage terminal in a low-impedance manner.
The switchable capacitances may be embodied as capacitors with a fixed capacitance value.
Compared with an embodiment having two transistors, each of which can connect a respective switchable capacitance to the supply voltage terminal, the described embodiment of activating the switchable capacitances in the case of a symmetrically constructed oscillator has the advantage that, on the one hand, a smaller series resistance of the switching unit takes effect between the switchable capacitances, namely that of the first switching means, and, at the same time, in the event of the switchable capacitances being deactivated, a smaller parasitic capacitance of the switching unit takes effect, so that overall the capacitance ratio between the two switching states is larger and the ratio of the oscillation frequencies of the oscillator circuit between two switching states is thus also larger in frequency terms. Since the two further switching means only effect a potential connection to the supply voltage and can therefore be made very small, the oscillator circuit pr
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Mis David C.
Stemer Werner H.
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