MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...
MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...
MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...
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oscillators (shown in the upper and lower half <strong>of</strong> the layout). Each LC oscillator is alsosymmetrical about the vertical. In both Fig. 94 and Fig. 95, the switchable-capacitorarray (a) which connects to the inductor (b) and varactor (c) to form the LC tank. Theinductors <strong>of</strong> the two LC oscillators are put apart to reduce the magnetic couplingbetween them because the coupling will force the two oscillators oscillate in phaseinstead <strong>of</strong> with quadrature phase difference. However, the large separation may result inthe poor matching between the two LC tanks in the two oscillators. The cross-coupledifferential pair (d) is used to compensate the loss <strong>of</strong> the LC tank. The shared currentsource (e) provides the current for both LC oscillators. There are a small couplingtransistors as a ring oscillator (f) to keep the quadrature phase between the two LCoscillators. The arrow pointing into the center the voltage-controlled oscillator in thelayout shows the biases, varactor tuning signal, digital control line <strong>of</strong> switchablecapacitorarray, power supply line and ground. The arrow pointing out shows theoutputs <strong>of</strong> the voltage-controlled oscillator. The whole voltage-controlled oscillator issurround by a p guard ring and a n-well ring (dashed line) in order to reduce thesubstrate noise from other circuits outside. There are also a SSB mixer (h) and outputbuffer to pad (i) for the quadrature phase and gain matching measurement and the phasenoise measurement.97