Systems, methods, and apparatus for controlling oscillator frequency response
A method may include generating, using an oscillator, a first signal having a frequency based on a current, generating, based on a second signal, a first portion of the current, the first portion of the current having a first frequency characteristic, and generating, based on the second signal, a second portion of the current, the second portion of the current having a second frequency characteristic. A gain of the first frequency characteristic may change based on a frequency of the second signal. The first frequency characteristic may include a first gain at a first frequency, and a second gain at a second frequency. The first gain may be greater than the second gain, and the second frequency may be greater than the first frequency. A phase of the first frequency characteristic may change based on a frequency of the second signal.
1 . A method comprising:
generating, using an oscillator, a first signal having a frequency based on a current;
generating, based on a second signal, a first portion of the current, the first portion of the current having a first frequency characteristic; and
generating, based on the second signal, a second portion of the current, the second portion of the current having a second frequency characteristic; and
controlling, using a calibration input circuit, a magnitude of at least one of the first portion of the current or the second portion of the current, wherein the calibration input circuit includes a differential circuit.
2 . The method of claim 1 further comprising:
controlling a frequency of the first signal by controlling an operating frequency of the oscillator; and
controlling, based on the frequency of the first signal, a gain of the first frequency characteristic.
3 . The method of claim 1 wherein the first frequency characteristic comprises:
a first gain at a first frequency of the first frequency characteristic; and
a second gain at a second frequency of the first frequency characteristic.
4 . The method of claim 3 wherein:
the first gain is greater than the second gain; and
the second frequency is greater than the first frequency.
5 . The method of claim 1 further comprising:
controlling a phase response of the first frequency characteristic as a function of frequency; and
controlling, based on the phase response of the first frequency characteristic, a gain of the first frequency characteristic.
6 . The method of claim 1 wherein the first frequency characteristic comprises:
a first phase shift at a first frequency; and
a second phase shift at a second frequency.
7 . The method of claim 6 wherein:
the first phase shift is in a first direction; and
the second phase shift is in a second direction.
8 . A circuit comprising:
an oscillator configured to generate a first signal having a frequency based on a current; and
a current generator configured to generate the current;
wherein the current generator comprises:
a first path configured to generate, based on a second signal, a first portion of the current, the first path having a first frequency characteristic; and
a second path configured to generate, based on the second signal, a second portion of the current, the second path having a second frequency characteristic;
and further comprising a calibration input circuit configured to control a contribution of at least one of the first portion of the current or the second portion of the current, wherein the calibration input circuit comprises a differential circuit.
9 . The circuit of claim 8 , wherein:
the first path comprises a first transistor configured to generate, based on the second signal, the first portion of the current; and
the second path comprises a second transistor configured to generate, based on the second signal, the second portion of the current.
10 . The circuit of claim 9 , wherein the second path comprises a filter configured to control, based on the second signal, the second transistor.
11 . The circuit of claim 1 , further comprising:
an input stage configured to generate a control signal based on a comparison of an input signal and a reference signal;
wherein the input stage comprises a differential pair of transistors and a current mirror load configured to:
(i) convert a differential output of the input stage to a single-ended current corresponding to the first portion of the current; and
(ii) generate a control node that drives the second path through a filter element.
12 . The circuit of claim 8 , wherein:
the first path is configured to generate, based on a third signal, the first portion of the current;
the second path is configured to generate, based on the third signal, the second portion of the current; and
the circuit further comprises an input stage configured to generate, based on the second signal, the third signal.
13 . The circuit of claim 12 , wherein the current is a first current, the third signal is a second current, and the current generator comprises a current mirror configured to:
generate, based on the second current, using the first path, a first portion of the first current; and
generate, based on the second current, using the second path, a second portion of the first current.
14 . The circuit of claim 12 , wherein the input stage is configured to generate, based on a comparison of the second signal and a fourth signal, the third signal.
15 . The circuit of claim 8 , further comprising a detector circuit configured to generate, based on a comparison of the first signal and a third signal, the second signal.
16 . The circuit of claim 14 , wherein:
the circuit has a loop bandwidth;
the first path has a pole at a pole frequency; and
the loop bandwidth is greater than the pole frequency.