Temperature compensation and coarse tune bank switches in a low phase noise VCO

摘要

The LC tank of a VCO includes a main varactor circuit and temperature compensation varactor circuit coupled in parallel with the main varactor circuit. The main varactor is used for fine tuning. The temperature compensation varactor circuit has a capacitance-voltage characteristic that differs from a capacitance-voltage characteristic of the main varactor circuit such that the effects of common mode noise across the two varactor circuits are minimized. The LC tank also has a plurality of switchable capacitor circuits provided for coarse tuning. To prevent breakdown of the main thin oxide switch in each of the switchable capacitor circuits, each switchable capacitor circuit has a capacitive voltage divider circuit that reduces the voltage across the main thin oxide switch when the main switch is off.

主权项

1. A circuit comprising:
a fine tune varactor circuit, the fine varactor circuit including:
a first varactor having a first terminal and a second terminal;a second varactor having a first terminal and a second terminal, wherein the second terminal of the second varactor and the second terminal of the first varactor are coupled together at a third node;a third varactor having a first terminal and a second terminal, wherein the first terminal of the third varactor and the first terminal of the first varactor are coupled together at a first node; anda fourth varactor having a first terminal and a second terminal, wherein the first terminal of the fourth varactor and the first terminal of the second varactor are coupled together at a second node, wherein the second terminal of the fourth varactor and the second terminal of the third varactor are coupled together at a fourth node; and a coarse tune capacitor circuit connected to the first varactor via the first node and connected to the second varactor via the second node, wherein the coarse tune capacitor circuit includes a plurality of switchable capacitor circuits, wherein a first of the plurality of switchable capacitor circuits includes:
a first transistor responsive to a first pair of control signals that is generated by a digital baseband integrated circuit, wherein the first pair of control signals is unique to the first of the plurality of switchable capacitor circuits; anda second transistor connected in parallel with a path that includes the first transistor, wherein the second transistor is responsive to a second pair of control signals that is generated by the digital baseband integrated circuit, wherein the second pair of control signals is common to each of the plurality of switchable capacitor circuits, and wherein each signal of the first pair of control signals and each signal of the second pair of control signals is generated independently.