Tuning circuit for inductor capacitor (LC) tank digitally controlled oscillator

摘要

In one embodiment, an apparatus includes a first circuit of a digitally controlled oscillator (DCO). The first circuit has a loss component. A second circuit is coupled to the first circuit and configured to transform a positive impedance into a negative impedance in series with a negative resistance. The negative impedance includes an adjustable reactive component used to adjust a frequency of an output signal of the DCO. An equivalent reactance seen by the first circuit is less than a reactance of the adjustable reactive component.

主权项

1. A digitally controlled oscillator (DCO) configured to generate a radio frequency (RF) output signal, the DCO comprising:
an inductor-capacitor (LC) tank circuit having a loss component, the LC tank configured to generate an output frequency of the RF output signal; an impedance transformer circuit configured to transform a positive impedance associated with the loss component into a negative impedance; and a tuning circuit configured to tune the output frequency of the RF output signal, wherein the impedance transformer circuit comprises
a first transistor,a second transistor cross-coupled with the first transistor,a third transistor, anda fourth transistor cross-coupled with the third transistor, wherein the third transistor and the fourth transistor are connected in parallel with the first transistor and the second transistor, wherein
a gate of the first transistor is connected to a drain of the second transistor, a gate of the second transistor is connected to a drain of the first transistor,the drain of the first transistor and the drain of the second transistor are connected to the LC tank circuit, anda source of the first transistor and a source of the second transistor are connected to the tuning circuit, and wherein the source of the first transistor is connected, via the tuning circuit, to a first current source configured to bias the first transistor, and wherein the source of the second transistor is connected, via the tuning circuit, to a second current source configured to bias the second transistor.