Voltage-Controlled Oscillators for High Data Rate Applications

Conclusions

In this chapter, two totally different types of oscillators have been presented. In a first section, a ringoscillator has been taken under consideration. The use of a four stage ringoscillator has the advantage of a directly available quadrature oscillator signal. It has been demonstrated analytically that the (4n-1)th harmonics of a quadrature square wave can be filtered out using a polyphase network. Two chips have been presented that incorporate a ringoscillator linearized using this technique. The first one is a single-channel upconvertor and the second one is a dual-channel upconvertor. Both are tailored for cable applications, with a useful frequency range of 100 MHz to 1.1 GHz. The major disadvantages of a ringoscillator, being a high phase noise and relatively high current consumption have become clear from the measurement results.

In a second section, some design issues concerning oscillators for RF frequencies have been discussed. The need for high symmetry on both floor plan level and building block level has been explained. It has been clarified that in some part of the design space of an LC oscillator the power is inverse proportional to the phase noise. More specifically, this happens when the resistance of the gain cell becomes the dominant source of phase noise in the LC tank. The reported behavior is in this case exactly the opposite of the otherwise generally valid proportionality between phase noise and power of an LC-tank based oscillator. Using the CYCLONE tool presented in Chapter 3, a 17 GHz VCO has been designed. The measurement results have been presented in this chapter and by comparison with other published work, it has been shown that the VCO can be truly considered as state-of-the-art.