Abstract: A VGA is provided that is designed to reduce or even eliminate entirely variations in phase response/shift with changes in gain. Compensation is made for parasitic capacitances of elements in the VGA that would otherwise cause variation in phase with changes in gain. An additional capacitance is introduced to the VGA to compensate for the sources of the parasitic capacitance. The technique for introducing the additional capacitance depends on the source of the parasitic capacitance being treated. The additional capacitance is introduced to one or more of transistor amplifier circuits in the VGA, wherein each transistor amplifier circuit has a different gain and one of the transistor amplifier circuits is selected depending on the desired gain of the VGA. These compensation techniques equalize the phase response of the transistor amplifier circuits (each having a different gain) so that regardless of which transistor amplifier circuit is selected, the phase shift will be substantially the same.

Abstract: A VCO having an automatic amplitude control circuit In the form of a sensing amplifier provided in the feedback loop to sense the oscillator amplitude and draw current away only when the positive peak voltage Is above a certain value. In general, any amplifier may be used in the feedback loop that outputs current proportional to a peak positive input (in a non-linear and asymmetric fashion with respect to the changing voltage). In one example, the amplifier in the feedback loop comprises first and second transistors that are set nominally in cut off and behave as class C amplifiers. The advantage of this amplifier transistor configuration is that the amplifier they form has a low load on the LC tank circuit and a high input impedance.

Abstract: A VCO having an automatic amplitude control circuit in the form of a sensing amplifier provided in the feedback loop to sense the oscillator amplitude and draw current away only when the positive peak voltage is above a certain value. In general, any amplifier may be used in the feedback loop that outputs current proportional to a peak positive input (in a non-linear and asymmetric fashion with respect to the changing voltage). In one example, the amplifier in the feedback loop comprises first and second transistors that are set nominally in cut off and behave as class C amplifiers. The advantage of this amplifier transistor configuration is that the amplifier they form has a low load on the LC tank circuit and a high input impedance.