Injection locking
Injection locking and injection pulling refer to the frequency effects that can occur when an oscillator is disturbed by a second oscillator operating at a nearby frequency. When the coupling is strong enough, and the frequencies near enough, the second oscillator can "capture" the first oscillator, causing it to have essentially identical frequency as the second. This is termed "injection locking". When the second oscillator merely disturbs the first but does not capture it, the effect is called "injection pulling". Injection locking and pulling effects are observed in numerous types of physical systems, however the terms are most often associated with electronic oscillators or laser resonators.
Injection locking has been used in beneficial and clever ways in the design of early television sets and oscilloscopes, allowing the equipment to be sync'd to external signals at a relatively low cost. Injection locking has also been used in high performance frequency doubling circuits. However, injection locking and pulling are serious pitfalls many cases of injection locking and pulling in electronic circuits are undesired due to unintended cross-talk between undesirable More recently, however, the topic has become of interest to engineers designing radio frequency integrated circuits when unintended cross-talk occurs between two or more frequency sources due to parasitic interference between frequency However unintended injection pulling and injection locking can bedevil electronic systems and lead to complex and undesirable frequency spectra, due to the unintended cross-talk of two or more oscillators in the system.
Injection: 17th century clocks to modern lasers
Injection pulling and injection locking can be observed in numerous physical systems where pairs of oscillators are coupled together. Perhaps the first to document these effects was Christiaan Huygens, the inventor of the pendulum clock, who was surprised to note that two of his pendulums became perfectly synchronized when hung from a common beam but kept slightly different time otherwise. Modern researchers have confirmed his suspicion that the pendulums were coupled by tiny back-and-forth vibrations in the wooden beam. The two clocks became injection locked to a common frequency (as a side note, it is not clear if one of the clocks dominated the other, or if they both drifted towards the frequency of the other and locked when they met).
In practice, however, the terms "injection locking" and "injection pulling", are rarely applied to mechanical systems but are more typically used to refer to high frequency systems where the oscillators operate in the RF, microwave, or optical wavelengths. See injection seeder for a description of how injection locking is used to improve the frequency spectrum of large lasers.
In the case of a VCO an injection-locking signal may override its low-frequency control voltage. When accidental and degrading, it's termed unwanted injection locking. When intentionally employed, injection locking provides a means to significantly reduce power consumption and possibly reduce phase noise in comparison to other frequency synthesizer and PLL design techniques. The main trade-offs are a narrower frequency range and an increase in die-size to accommodate on-chip inductors.
Injection-locked oscillator
An injection-locked oscillator (ILO) is usually based on cross-coupled LC oscillator. It has been employed for frequency division [1] or jitter reduction in PLL, with the input of pure sinusoidal waveform. It was employed in continuous mode clock and data recovery (CDR) or clock recovery to perform clock restoration from the aid of either preceding pulse generation circuit to convert non-return-to-zero (NRZ) data to pseudo-return-to-zero (PRZ) format[2] or nonideal retiming circuit residing at the transmitter side to couple the clock signal into the data.[3] Recently, the ILO was employed for burst mode clock recovery scheme.[4]
The operation of ILO is based on the fact that the local oscillation can be locked to the frequency and phase of external injection signal under proper conditions.
Unwanted injection locking
High-speed logic signals and their harmonics are potential threats to an oscillator. The leakage of these and other high frequency signals into an oscillator through a substrate concomitant with an unintended lock is unwanted injection locking.
Gain by injection locking
Injection locking can also provide a means of gain at a low power cost in certain applications.
See also
- Injection locked frequency divider
- Injection-locked PLL
- LC oscillator
- Electronic oscillator
- Burst mode clock and data recovery
References
- ^ M. Tiebout, "A CMOS direct injection-locked oscillator topology as high-frequency low-power frequency divider," IEEE Journal of Solid-State Circuits, vol. 39, pp. 1170-1174, 2004.
- ^ M. De Matos, J. B. Begueret, H. Lapuyade, D. Belot, L. Escotte, and Y. Deval, "A 0.25um SiGe receiver front-end for 5GHz applications," SBMO/IEEE MTT-S International Conference on Microwave and Optoelectronics 2005, pp. 213-217.
- ^ [54] T. Gabara, "An 0.25 μm CMOS injection locked 5.6 Gb/s clock and data recovery cell," in Symposium on Integrated Circuits and Systems Design 1999, pp. 84 - 87.
- ^ J. Lee and M. Liu, "A 20Gb/s burst-mode CDR circuit using injection-locking technique," in IEEE International Solid-State Circuits Conference (ISSCC), pp. 46-586, 2007.
Further reading
* Wolaver, Dan H. 1991. Phase-Locked Loop Circuit Design, Prentice Hall, ISBN 0-13-662743-9, pages 95-105
- Adler, R. (1973). "A study of locking phenomena in oscillators". Proceedings of the IEEE. 61 (10): 1380–1385.
{{cite journal}}: Unknown parameter|month=ignored (help) - Kurokawa, K. (1973). "Injection locking of microwave solid-state oscillators". Proceedings of the IEEE. 61 (10): 1386–1410.
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* Lee, Thomas H. 2004. The Design of CMOS Radio-Frequency Integrated Circuits, Cambridge, ISBN 0-521-83539-9, pages 563-566