Patent Application
20110215876
The present invention concerns voltage controlled oscillators in general, and specifically an improved self-injection locked voltage controlled oscillator.
As one of the key components in RF front-end devices, a voltage controlled oscillator (VCO) with low phase noise is highly demanded. Injection locking is a technique that is used to reduce the phase noise [1]-[4] of a VCO. It is a type of forced oscillation where a signal is injected into the oscillator and “locks” the oscillator to the frequency and phase of the injected signal under proper conditions.
Self-injection locking is a special type of the injection locking technique, where the injected signal comes from the oscillator itself instead of from an external source. An early self-injection-locking arrangement is shown in
In the above-mentioned known solutions, the output signal is split into two and one of them is delayed via signal propagation through the delay line and then is injected into the oscillator. The delay must be sufficiently long, so that the delayed signal is uncorrelated with the un-delayed signal [1, 5]. Typically, several nano seconds delay is required for GHz oscillators. This makes it difficult to implement the delay line on a substrate, such as Si or glass substrate, since the resulting component would be too large and too costly.
As described above, one problem with the above-mentioned solutions is the large substrate area consumed by the delay line, and consequently of the entire oscillator device. Thus, shortening the delay line becomes a practical issue for self-injection locked VCOs.
An object of the present invention is thus to provide a self-injection oscillator device with reduced length of the delay line.
Basically, an improved self injection locked voltage controlled oscillator arrangement (1) comprises a pair of coupled first and second voltage controlled oscillator devices (21, 22) arranged on a chip (2), an amplifier device (23) arranged on said chip (2), and an off-chip delay line (10) arranged with one terminal connected to an output terminal of said coupled first and second voltage controlled oscillators (21, 22), and one terminal adapted to reflect a signal from said output terminal, to provide an improved VCO arrangement (1).
Advantages of the present invention include
The invention, together with further objects and advantages thereof, may best be understood by referring to the following description taken together with the accompanying drawings, in which:
In the present disclosure, embodiments of a novel arrangement for a self-injection-locked VCO are disclosed.
With reference to
The phase noise of an injection locked VCO depends on the amplitude of the injection signal and the delay time, which near the carrier frequency is given by [5]:
Where Airy and A denote the amplitude of the VCO signal with and without self-injection, respectively. Similarly, |δ{tilde over (θ)}| and |δ{tilde over (θ)}0| denote the phase noise spectra in the two cases, respectively; T is the delay time;
Furthermore, as shown in
A hybrid solution may be used to implement the proposed arrangement. A self-injection-locked VCO module 1, for instance, can be built using semiconductor chip consisting of a coupled VCO pair 21, 22, with an integrated amplifier 23 and an off-chip delay line 10 built on a separate substrate. The chip 2 and the substrate may be interconnected either by bounded wires or flip-chip bumps, or some other connection means.
It is evident that the above described technique is not limited to any particular type of oscillators; therefore a few variants of embodiments are disclosed and discussed below.
With reference to
In order to make the above described circuit more symmetric, a source- coupled transistor pair can be applied to form a differential amplifier, as shown in the embodiment of
Finally, it should be emphasized that the proposed self-injection VCO is not limited to the Hartley VCO topology. In principle, any type of VCOs may be applicable.
By implementing the above mentioned combination of on-chip coupled oscillators, on-chip amplifier, and off chip reflective type delay line a number of key features are achieved, as well as a plurality of advantageous properties.
In summary, a pair of coupled VCOs is integrated with either a single-ended or a differential amplifier to provide an improved self-injection-locked oscillator configuration. The integration of the amplifier boosts the power level of the injected signal without necessarily requiring any additional discrete components, The short/ open termination or reflective adaptation of the delay line eliminates the need of a circulator (and potentially a power splitter as well) when the feedback signal is preferred to be injected into the VCO at the same port as the outgoing signal, as in ref [1]-[2]. Finally, as compared to the conventionally used propagation-type delay line, the reflection-type delay of the present invention practically shortens the required delay-line length by half.
Advantages of the present invention comprise:
The improved self-injection locked VCO according to the present invention can be implemented in any semiconductor technology, e.g. Si (CMOS, bipolar), GaAs (HBT, HEMT), etc.
It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/065765 | 11/18/2008 | WO | 00 | 5/4/2011 |
