Current reference generator and associated method

Abstract

The invention relates to a current reference generator and an associated method. According to various embodiments of the present disclosure, a circuit for providing a reference current to a device having a first current controlled oscillator (CCO) is provided. In some embodiments, the circuit includes a reference circuit and a feedback loop circuit. The feedback loop circuit includes: a differential circuit that receives an input voltage from a reference circuit and provides an output current; a second CCO receiving the output current from the differential circuit and generating an output frequency in response; the frequency divider circuit is used for dividing the output frequency into a feedback frequency; and a feedback switched capacitor resistor circuit that provides a feedback voltage to the differential circuit based on the feedback frequency. The second CCO has substantially matched performance with the first CCO. The differential circuit adjusts its output current based on a difference between the input voltage and the feedback voltage.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority and the benefit of U.S. Provisional Patent Application Serial No. 63 / 603,954, titled "CURRENT REFERENCE GENERATOR AND ASSOCIATED METHOD", filed on November 29, 2023, which is incorporated herein by reference in its entirety. Technical field

[0003] Example embodiments of the present disclosure generally relate to digitally controlled oscillators, and more particularly to circuits, integrated circuits, methods, systems, and devices for providing a reference current to a digitally controlled oscillator. Background art

[0004] In many applications such as phase - locked loops, it is necessary to generate a frequency. This is typically achieved using a digitally controlled oscillator (DCO) or a voltage - controlled oscillator (VCO). The DCO takes a digital input and converts it into a frequency, and the VCO takes a voltage input and converts it into a frequency.

[0005] A DCO essentially includes a digital - to - analog converter (DAC) and a current - controlled oscillator (CCO). To generate a frequency, the DCO requires a current reference. The reference current requirements of the CCO in the DCO for generating the same frequency vary with the process, voltage, and / or temperature (PVT) of the CCO. That is, as the PVT changes, different ranges of reference current are required to provide the same frequency.

[0006] Conventional current references generate a current that is independent of the CCO current requirements. Depending on the CCO requirements, the conventional current reference may not provide the current required for the CCO to produce the desired frequency. Thus, a conventional DAC will make the necessary changes to the input of the CCO. However, this requires a larger and more complex DAC, which takes up more space and requires more complex code to control.

[0007] The applicant has found many technical challenges and difficulties associated with providing a reference current to a digitally controlled oscillator. Through applied effort, ingenuity, and innovation, the applicant has solved the problems associated with providing a reference current to a digitally controlled oscillator by developing the solutions implemented in the present disclosure, which will be described in detail below. Summary of the invention

[0008] Various embodiments described herein relate to circuits, integrated circuits, methods, devices, and systems for providing a reference current to a digitally controlled oscillator (DCO) or a voltage - controlled oscillator (VCO).

[0009] According to various embodiments of the present disclosure, a circuit for providing a reference current to a device having a first current controlled oscillator (CCO) is provided. In some embodiments, the circuit includes a reference circuit that provides an input voltage or an input current based on a reference frequency and a feedback loop circuit. The feedback loop circuit includes: a differential circuit having a first input terminal that receives the input voltage or the input current from the reference circuit and provides an output current; a second CCO that receives the output current from the differential circuit and in response generates an output frequency, the second CCO being adapted to have performance substantially matching that of the first CCO; a frequency divider circuit for dividing the output frequency into a feedback frequency; and a feedback switched capacitor resistor circuit that provides a feedback voltage or a feedback current to a second input terminal of the differential circuit based on the feedback frequency. The differential circuit adjusts its output current based on the difference between the input voltage and the feedback voltage or the difference between the input current and the feedback current. The differential circuit is adapted to provide the output current to a device having a first CCO as a reference current. Since the second CCO has performance substantially matching that of the first CCO, the feedback frequency is adapted to be substantially equal to a divided version of the output frequency of the device having the first CCO.

[0010] In some embodiments, the device having the first CCO includes a digitally controlled oscillator (DCO) or a voltage controlled oscillator (VCO).

[0011] In some embodiments, the frequency divider circuit is selected such that when the input voltage is equal to the feedback voltage or the input current is equal to the feedback current, the feedback frequency is equal to the reference frequency.

[0012] In some embodiments, the second CCO is adapted to have substantially the same structure as the first CCO.

[0013] In some embodiments, the differential circuit includes a differential amplifier and a voltage-to-current converter connected to an output terminal of the differential amplifier.

[0014] In some embodiments, the reference circuit includes a reference switched capacitor resistor circuit.

[0015] In some embodiments, the input voltage provided to the first input terminal of the differential circuit is a reference voltage, the reference circuit further includes a differential amplifier and a voltage-to-current converter connected to an output terminal of the differential amplifier, the reference voltage is provided to the first input terminal of the differential amplifier, the reference frequency and a first current from the voltage-to-current converter are input to the reference switched capacitor resistor circuit to generate a first voltage provided to the second input terminal of the differential amplifier, the first current from the voltage-to-current converter is mirrored to the feedback loop circuit to provide a second current, and the second current and the feedback frequency are input to the feedback switched capacitor resistor circuit to generate a feedback voltage provided to the differential circuit.

[0016] In some embodiments, a reference frequency and a first current are input to a reference switched capacitor resistor circuit to generate an input voltage provided to a first input terminal of a differential circuit, and a feedback frequency and a second current equal to the first current are input to a feedback switched capacitor resistor circuit to generate a feedback voltage provided to a second input terminal of the differential circuit.

[0017] In some embodiments, the reference circuit further includes a first differential amplifier and a first voltage-to-current converter connected to an output terminal of the first differential amplifier. A reference voltage is provided to a first input terminal of the first differential amplifier. A reference frequency and a first current from the first voltage-to-current converter are input to the reference switched capacitor resistor circuit to generate a first voltage provided to a second input terminal of the first differential amplifier. The first current from the first voltage-to-current converter is an input current provided to a first input terminal of the differential circuit. The feedback loop circuit further includes a second differential amplifier and a second voltage-to-current converter connected to an output terminal of the second differential amplifier. A reference voltage is provided to a first input terminal of the second differential amplifier. A second current from the second voltage-to-current converter is input to the feedback switched capacitor resistor circuit to generate a second voltage provided to a second input terminal of the second differential amplifier. And the second current from the second voltage-to-current converter is a feedback current to a second input terminal of the differential circuit.

[0018] According to various embodiments of the present disclosure, a method of providing a reference current to a device having a first current controlled oscillator (CCO) is provided. In some embodiments, the method includes: providing, by a reference circuit, an input voltage or an input current to a first input terminal of a differential circuit of a feedback loop circuit based on a reference frequency; providing, by the differential circuit, an output current; receiving, by a second CCO, the output current from the differential circuit, the second CCO being adapted to have performance substantially matching that of the first CCO; generating, by the second CCO, an output frequency in response to the received output current; dividing, by a frequency divider circuit, the output frequency into a feedback frequency; providing, by a feedback switched capacitor resistor circuit, a feedback voltage or a feedback current to a second input terminal of the differential circuit based on the feedback frequency; adjusting, by the differential circuit, its output current based on a difference between the input voltage and the feedback voltage or a difference between the input current and the feedback current; and providing, by the differential circuit, the output current to the device having the first CCO as a reference current. Since the second CCO has performance substantially matching that of the first CCO, the feedback frequency is adapted to be substantially equal to a frequency-divided version of the output frequency of the device having the first CCO.

[0019] The above - mentioned invention content is only provided to summarize some exemplary embodiments and to provide a basic understanding of some aspects of the present disclosure. Thus, it will be recognized that the above - mentioned embodiments are merely examples and should not be construed as narrowing the scope or spirit of the present disclosure in any way. It will also be recognized that the scope of the present disclosure covers many potential embodiments in addition to the embodiments outlined herein, some of which will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The description of the illustrative embodiments may be read in conjunction with the accompanying drawings. It will be recognized that, for simplicity and clarity of illustration, the elements shown in the figures are not necessarily drawn to scale unless otherwise described. For example, the dimensions of some elements may be exaggerated relative to other elements unless otherwise described. The figures presented herein illustrate and describe embodiments in conjunction with the teachings of the present disclosure, and in the figures presented herein:

[0021] Figure 1 A block diagram of an example circuit for providing a reference current to a numerically controlled oscillator in accordance with some embodiments of the present disclosure is illustrated;

[0022] Figure 2 and Figure 3 A block diagram of an example circuit for providing a reference current to a numerically controlled oscillator in accordance with alternative embodiments of the present disclosure is illustrated; and

[0023] Figure 4 is an example flowchart of an example method for providing a reference current to a numerically controlled oscillator in accordance with an example embodiment of the present disclosure. DETAILED DESCRIPTION

[0024] Some embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the present disclosure are shown. In fact, these disclosures may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout.

[0025] As used herein, terms such as "front", "rear", "top", etc. are used for illustrative purposes in the examples provided below to describe the relative positions of certain components or portions of components. Additionally, in accordance with the present disclosure, as will be apparent to those of ordinary skill in the art, the terms "substantially" and "approximately" indicate that the referenced element or associated description is accurate within the applicable engineering tolerances.

[0026] As used herein, the term "comprising" means including but not limited to and shall be construed in the manner it is commonly used in the patent context. The use of broader terms such as including, containing, and having shall be understood to provide support for narrower terms such as consisting of, consisting essentially of, and consisting substantially of.

[0027] Phrases such as "in one embodiment", "according to one embodiment", etc. generally mean that the particular feature, structure, or characteristic following such phrase can be included in at least one embodiment of the present disclosure and can be included in more than one embodiment of the present disclosure (importantly, such phrases do not necessarily refer to the same embodiment).

[0028] The word "example" or "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0029] If the specification states that a component or feature "may", "can", "might", "should", "will", "preferably", "possibly", "generally", "optionally", "for example", "often", or "may" (or other such language) be included or have a certain characteristic, then the particular component or feature is not required to be included or have that characteristic. Such a component or feature may optionally be included in some embodiments, or it may be excluded.

[0030] Various embodiments of the present disclosure are based on, for example but not limited to, providing example circuits, integrated circuits, methods, devices, and systems for providing a current reference for a DCO to track PVT variations of a CCO, to overcome the above technical challenges and difficulties and to provide various technical improvements and advantages. In various embodiments, the method helps, for example, in a phase-locked loop (PLL) where a current reference is needed to use a DCO or a voltage-controlled oscillator (VCO) to generate a desired frequency. In an analog PLL, the current reference is used for the charge pump current, and the loop filter converts it into a voltage input for the VCO. In a digital PLL, the current reference serves as a reference for a digital-to-analog converter (DAC).

[0031] Various embodiments of the present disclosure provide a circuit and a method for generating a current reference for a DCO or a VCO to track PVT variations of a CCO. In various embodiments, a feedback loop uses a copy or replica of the CCO of the DCO / VCO to predict potential variations in the output of the CCO of the DCO / VCO due to PVT variations.

[0032] In various embodiments, a reference circuit provides an input voltage or input current to a differential circuit having a feedback loop circuit that can be referred to as a replica CCO. In various embodiments, the replica CCO has performance that substantially matches that of the CCO of the DCO / VCO and is thus affected by any PVT variations in substantially the same manner. In various embodiments, the replica CCO has substantially the same structure and components as the CCO of the DCO / VCO.

[0033] In various embodiments, the replica CCO receives an output current from the differential circuit and generates an output frequency. In various embodiments, the output frequency is divided and provided to a switched capacitor resistor circuit that in turn provides a feedback voltage or feedback current to the differential circuit. In various embodiments, the differential circuit adjusts its output current based on the difference between the input voltage and the feedback voltage or the difference between the input current and the feedback current. Thus, the output current from the differential circuit is adjusted in response to PVT variations of the replica CCO. In various embodiments, the output current from the differential circuit is provided as a reference current to the DCO of a digital PLL to enable a desired frequency output. Since the replica CCO is affected by any PVT variations in substantially the same manner as the CCO of the DCO / VCO, the provided reference current compensates (at least in part) for the PVT variations.

[0034] Figure 1 A block diagram illustrates an example circuit that uses a replica CCO to provide a current reference for a DCO that tracks PVT variations of the CCO of the DCO as described herein. While various embodiments of the present disclosure provide circuits and methods for generating a current reference for a DCO or VCO, for simplicity, embodiments of the present disclosure will be described herein in connection with generating a current reference for a DCO.

[0035] As Figure 1 seen, example circuit 100 includes a reference circuit portion 102 and a feedback loop circuit portion 120. The reference circuit portion 102 provides a voltage (or current in an alternative embodiment described below) to the feedback loop circuit portion 120. In the illustrated embodiment, the reference circuit portion 102 includes a differential amplifier 104, a voltage-to-current (V2I) converter 106 connected to the output of the differential amplifier 104, and a switched capacitor resistor circuit 108 (referred to herein as the "reference switched capacitor resistor circuit" due to its location in the reference circuit) connected to the output of the V2I converter 106. The reference switched capacitor resistor circuit 108 has a capacitance C SW1 .

[0036] In the illustrated embodiment, the reference voltage V REFis provided to the first input of the differential amplifier 104. In some embodiments, Vref comes from a powered resistor divider or can be a BangGap voltage. In the illustrated embodiment, the reference frequency f REF (which can also be referred to as the input frequency) is input to the reference switched capacitor resistor circuit 108. In various embodiments, the input frequency f REF is the PLL input frequency. In the illustrated embodiment, the current output I 1 from the V2I converter 106 is also input to the reference switched capacitor resistor circuit 108. The resistance of the switched capacitor resistor is 1 / fC, so the resistance of the reference switched capacitor resistor circuit 108 is 1 / (f REF x C SW1 ). With an input current of I 1 , the voltage V 1 across the reference switched capacitor resistor circuit 108 is equal to I 1 / (f REF x C SW1 ). In the illustrated embodiment, the voltage V 1 is provided to the second input of the differential amplifier 104 as feedback to help maintain the current I 1 at a stable level. In the illustrated embodiment, the current I 1 is also mirrored to the feedback loop circuit portion 120 via a voltage-to-current (V2I) converter 136.

[0037] In the illustrated embodiment, the feedback loop circuit portion 120 includes a V2I converter 136, a differential circuit portion 122, a replica CCO 130, a frequency divider circuit portion 132, and a switched capacitor resistor circuit 134 (referred to herein as the "feedback switched capacitor resistor circuit" due to its position in the feedback loop circuit). In the illustrated embodiment, the differential circuit portion 122 includes a differential amplifier 124 and a V2I converter 126. As described above, the replica CCO 130 has performance that substantially matches that of the CCO 158 of the DCO 150 and is thus affected by any PVT variations in substantially the same way.

[0038] In the illustrated embodiment, the reference voltage V REF is provided to the first input of the differential amplifier 124. In the illustrated embodiment, the current output from the V2I converter 126 is input to the replica CCO 130, which generates an output frequency. In the illustrated embodiment, the output frequency is divided by the frequency divider circuit portion 132. In various embodiments, the frequency divider circuit portion 132 divides the output frequency from the replica CCO 130 such that when the feedback loop is operating and compensating for any PVT variations, the divided frequency fDIV is equal to the reference frequency f REF (as described below). In the illustrated embodiment, the divided frequency f DIV is provided to the feedback switched capacitor resistor circuit 134. In the illustrated embodiment, the current output from the V2I converter 126 that is input to the replica CCO 130 is also output as a reference current 160 to the DCO 150 (the DCO 150 will be described further below).

[0039] The feedback switched capacitor resistor circuit 134 has a capacitance C SW2 . The resistance of the switched capacitor resistor is 1 / fC, and thus the resistance of the feedback switched capacitor resistor circuit 134 is 1 / (f REF x C SW2 ). In the case where the input current from the V2I converter 136 is I 2 , the voltage V 2 across the feedback switched capacitor resistor circuit 134 is equal to I 2 / (f DIV x C SW2 ). In the illustrated embodiment, the voltage V 2 is provided as feedback to the second input of the differential amplifier 124.

[0040] In various embodiments, the capacitance C SW1 of the reference switched capacitor resistor circuit 108 is equal to the capacitance C SW2 of the feedback switched capacitor resistor circuit 134. 1 In various embodiments, the current I 2 provided to the reference switched capacitor resistor circuit 108 is the same as the current I 1 provided to the feedback switched capacitor resistor circuit 134 because I 2 comes from a feedback loop including the differential amplifier 104 and I 1 is made equal to I SW1 . Since C SW2 is equal to C 1 and I 2 is equal to I 2 , if the feedback loop circuit portion 120 successfully makes the voltage V REF across the feedback switched capacitor resistor circuit 134 equal to the reference voltage V DIV , then the divided frequency f REF is equal to the reference frequency f

[0041] In various embodiments, if the output frequency of replica CCO 130 changes due to PVT variations (which are substantially the same as the PVT variations that occur in CCO 158 of DCO 150, as described above), the voltage V across feedback switched capacitor resistor circuit 134 is 2 In response, the differential amplifier 124 will compare the two voltages (V REF and V 2 ), and attempts to make the voltage V across the feedback switched capacitor resistor circuit 134 by adjusting its output voltage to the V2I converter 126 2 Equal to the reference voltage V REF , which changes the current to the replica CCO 130, and thus changes the output of the replica CCO 130. Since the current output from the V2I converter 126 that is input to the replica CCO 130 is also output to the DCO 150 as the reference current 160, the adjustment that the differential amplifier 124 will make to its output in response to PVT variations will also result in a corresponding change in the reference current 160 provided to the DCO 150. In this regard, the circuit 100 compensates for some or all of the PVT variations that occur in the CCO 158 of the DCO 150.

[0042] In the illustrated embodiment, the DCO 150 includes a current mirror 152 (which in turn includes a plurality of V2I converters 154), a DAC 156, and a CCO 158. The DCO 150 outputs a desired frequency f based on a supplied reference current 160. DCO The reference current 160 from the circuit 100 to the DCO 150 is mirrored via the current mirror 152 and provided to the DAC 156, which in turn provides the necessary signals to the CCO 158. Since the reference current 160 from the circuit 100 to the DCO 150 has already been adjusted to correct for PVT variations, the DAC 156 does not need to adjust the reference current (or only needs to make minor adjustments), so the DAC can be much smaller and simpler in this case.

[0043] Figure 2 1 is a block diagram of an example circuit for providing a current reference for a DCO that tracks PVT variations of the CCO of the DCO using a replica CCO according to an alternative embodiment of the present disclosure. Figure 2 As shown in FIG. 2 , the exemplary circuit 200 includes a reference circuit portion 202 and a feedback loop circuit portion 220. The reference circuit portion 202 provides a voltage V to the feedback loop circuit portion 220. 1 As a reference voltage. In the illustrated embodiment, the reference circuit portion 202 includes an output current I 1Current source 210 and a switched capacitor resistor circuit 208 connected to the current source 210 (referred to herein as the "reference switched capacitor resistor circuit" due to its position in the reference circuit). The reference switched capacitor resistor circuit 208 has a capacitance C SW1 .

[0044] In the illustrated embodiment, a reference frequency f REF (which may also be referred to as the input frequency) is input to the reference switched capacitor resistor circuit 208. In various embodiments, the input frequency f REF is an external input frequency. In the illustrated embodiment, a current I 1 from the current source 210 is input to the reference switched capacitor resistor circuit 208. The resistance of the switched capacitor resistor is 1 / fC, and thus the resistance of the reference switched capacitor resistor circuit 208 is 1 / (f REF x C SW1 ). In the case where the input current is I 1 , the voltage V 1 across the reference switched capacitor resistor circuit 208 is equal to I 1 / (f REF x C SW1 ). In the illustrated embodiment, the voltage V 1 is provided to the first input of a differential circuit portion 222 of a feedback loop circuit portion 220 (described further below).

[0045] In the illustrated embodiment, the feedback loop circuit portion 220 includes a current source 238 that outputs a current I 2 , a differential circuit portion 222, a replica CCO 230, a frequency divider circuit portion 232, and a switched capacitor resistor circuit 234 (referred to herein as the "feedback switched capacitor resistor circuit" due to its position in the feedback loop circuit). In the illustrated embodiment, the differential circuit portion 222 includes a differential amplifier 224 and a V2I converter 226. As described above, the replica CCO 230 has performance that substantially matches that of the CCO 158 of the DCO 150, and is thus affected by any PVT variations in substantially the same manner.

[0046] In the illustrated embodiment, a voltage V 1Is provided to the first input terminal of the differential amplifier 224. In the illustrated embodiment, the current output from the V2I converter 226 is input to the replica CCO 230, which generates an output frequency. In the illustrated embodiment, the output frequency is divided by the divider circuit section 232. In various embodiments, the divider circuit section 232 divides the output frequency from the replica CCO 230 such that when the feedback loop is operating and compensating for any PVT variations, the divided frequency f DIV Is equal to the reference frequency f REF (as described below). In the illustrated embodiment, the divided frequency f DIV Is provided to the feedback switched capacitor resistor circuit 234. In the illustrated embodiment, the current output from the V2I converter 226 that is input to the replica CCO 230 is also output as a reference current 260 to the DCO 150 (the DCO 150 is further described above).

[0047] The feedback switched capacitor resistor circuit 234 has a capacitance C SW2 . The resistance of the switched capacitor resistor is 1 / fC, so the resistance of the feedback switched capacitor resistor circuit 234 is 1 / (f REF x C SW2 ). In the case where the input current from the current source 238 is I 2 , the voltage V 2 across the feedback switched capacitor resistor circuit 234 is equal to I 2 / (f DIV x C SW2 ). In the illustrated embodiment, the voltage V 2 Is provided to the second input terminal of the differential amplifier 224 as feedback.

[0048] In various embodiments, the capacitance C SW1 of the reference switched capacitor resistor circuit 208 is equal to the capacitance C SW2 of the feedback switched capacitor resistor circuit 234. In various embodiments, the current I 1 provided to the reference switched capacitor resistor circuit 208 is the same as the current I 2 provided to the feedback switched capacitor resistor circuit 234. Since C SW1 is equal to C SW2 and I 1 is equal to I 2 , if the feedback loop circuit section 220 successfully makes the voltage V 2 across the feedback switched capacitor resistor circuit 234 equal to the voltage V 1 from the reference circuit section 202, then the divided frequency f DIV is equal to the reference frequency fREF .

[0049] In various embodiments, if the output frequency of replica CCO 230 changes due to PVT variations (which will be substantially the same as the PVT variations that occur in CCO 158 of DCO 150, as described above), then the voltage V across feedback switched capacitor resistor circuit 234 is 2 In response, the differential amplifier 224 will compare the two voltages (V 1 and V 2 ), and attempts to make the voltage V across the feedback switched capacitor resistor circuit 234 by adjusting its output voltage to the V2I converter 226 2 is equal to the voltage V from the reference circuit portion 202 1 , which changes the current to the replica CCO 230, and thus changes the output of the replica CCO 230. Since the current output from the V2I converter 226 that is input to the replica CCO 230 is also output to the DCO 150 as the reference current 260, the adjustment that the differential amplifier 224 will make to its output in response to the PVT variation will also cause a corresponding change in the reference current 260 provided to the DCO 150. In this regard, the circuit 200 compensates for some or all of the PVT variations that occur in the CCO 158 of the DCO 150. Since the reference current 260 from the circuit 200 to the DCO 150 has already been adjusted to correct for the PVT variations, the DAC 156 does not need to adjust the reference current (or only needs to make a minor adjustment), so the DAC 156 can be much smaller and simpler in this case.

[0050] Figure 3 1 is a block diagram of an example circuit for providing a current reference for a DCO that tracks PVT variations of the CCO of the DCO using a replica CCO according to an alternative embodiment of the present disclosure. Figure 3 As seen in , the example circuit 300 includes a reference circuit portion 302 and a feedback loop circuit portion 320. The reference circuit portion 302 provides current to the feedback loop circuit portion 320. In the illustrated embodiment, the reference circuit portion 302 includes a differential amplifier 304, a voltage-to-current (V2I) converter 306 connected to the output of the differential amplifier 304, and a switched capacitor resistor circuit 308 (referred to herein as a "reference switched capacitor resistor circuit" due to its position in the reference circuit) connected to the output of the V2I converter 306. The reference switched capacitor resistor circuit 308 has a capacitance C SW1 .

[0051] In the embodiment shown, the reference voltage V REFis provided to the first input of the differential amplifier 304. In some embodiments, Vref comes from a powered resistor divider or can be a BangGap voltage. In the illustrated embodiment, the reference frequency f REF (which can also be referred to as the input frequency) is input to the reference switched capacitor resistor circuit 308. In various embodiments, the input frequency f REF is an external input frequency. In the illustrated embodiment, the current output I 1 from the V2I converter 306 is also input to the reference switched capacitor resistor circuit 308. The resistance of the switched capacitor resistor is 1 / fC, so the resistance of the reference switched capacitor resistor circuit 308 is 1 / (f REF x C SW1 ). With an input current of I 1 , the voltage V 1 across the reference switched capacitor resistor circuit 308 is equal to I 1 / (f REF x C SW1 ). In the illustrated embodiment, the voltage V 1 is provided to the second input of the differential amplifier 304 as feedback to help maintain the current I 1 at a stable level. In the illustrated embodiment, the current I 1 is provided to the first input of the differential circuit portion 322 (described further below) of the feedback loop circuit portion 320 as a reference current.

[0052] In the illustrated embodiment, the feedback loop circuit portion 320 includes a differential amplifier 340, a voltage-to-current (V2I) converter 336 connected to the output of the differential amplifier 340, a differential circuit portion 322, a replica CCO 330, a frequency divider circuit portion 332, and a switched capacitor resistor circuit 334 (referred to herein as the "feedback switched capacitor resistor circuit" due to its position in the feedback loop circuit). In the illustrated embodiment, the differential circuit portion 322 includes a differential transimpedance amplifier 324 and a V2I converter 326. As described above, the replica CCO 330 has performance that substantially matches that of the CCO 158 of the DCO 150 and is thus affected by any PVT variations in substantially the same manner.

[0053] In the illustrated embodiment, the current I 1Is provided to the first input terminal of the differential transimpedance amplifier 324 as a reference current. In the illustrated embodiment, the current output from the V2I converter 326 is input to the replica CCO 330, which generates an output frequency. In the illustrated embodiment, the output frequency is divided by the divider circuit section 332. In various embodiments, the divider circuit section 332 divides the output frequency from the replica CCO 330 such that when the feedback loop is operating and compensating for any PVT variations (as described below), the divided frequency f DIV Is equal to the reference frequency f REF 。In the illustrated embodiment, the divided frequency f DIV Is provided to the feedback switched capacitor resistor circuit 334. In the illustrated embodiment, the current output from the V2I converter 326 that is input to the replica CCO 330 is also output as a reference current 360 to the DCO 150 (or to the charge pump of an analog PLL) (the DCO 150 will be further described below).

[0054] In the illustrated embodiment, the current I 1 Is provided to the first input terminal of the differential circuit section 322. In the illustrated embodiment, the current output I 2 From the V2I converter 336 is also input to the feedback switched capacitor resistor circuit 334. The feedback switched capacitor resistor circuit 334 has a capacitance C SW2 。The resistance of the switched capacitor resistor is 1 / fC, so the resistance of the feedback switched capacitor resistor circuit 334 is 1 / (f REF x C SW2 ). With an input current of I 2 , the voltage V 2 Across the feedback switched capacitor resistor circuit 334 is equal to I 2 / (f REF x C SW2 ). In the illustrated embodiment, the voltage V 2 Is provided as feedback to the second input terminal of the differential amplifier 340 to help maintain the current I 2 At a stable level. In the illustrated embodiment, the current I 2 Is provided as feedback to the second input terminal of the differential transimpedance amplifier 324.

[0055] In various embodiments, the capacitance C SW1 Of the reference switched capacitor resistor circuit 308 is equal to the capacitance C SW2 Of the feedback switched capacitor resistor circuit 334. In various embodiments, if the output frequency of replica CCO 330 changes due to PVT variations (as described above, which will be substantially the same as the PVT variations occurring in CCO 158 of DCO 150), then the voltage V across feedback switched capacitor resistor circuit 334 2 will change correspondingly. In response, differential amplifier 340 will compare these two voltages (V REF and V 2 ), and attempt to make the voltage V across feedback switched capacitor resistor circuit 334 equal to the reference voltage V 2 by adjusting its output voltage to V2I converter 336 (which changes the current I 2 to the feedback switched capacitor resistor circuit 334 and the second input of differential transimpedance amplifier 324). In response, differential transimpedance amplifier 324 will compare these two currents (I REF and I 1 ), and attempt to make these two currents equal by adjusting its output voltage to V2I converter 326 (which changes the current to replica CCO 330 and thus changes the output of replica CCO 330). 2

[0056] Since the current output from V2I converter 326 that is input to replica CCO 330 is also output as reference current 360 to DCO 150, the adjustment of the output of differential transimpedance amplifier 324 in response to PVT variations will also cause a corresponding change in the reference current 360 provided to DCO 150. In this regard, circuit 300 compensates for some or all of the PVT variations occurring in CCO 158 of DCO 150. Since the reference current 360 from circuit 300 to DCO 150 has been adjusted to correct for PVT variations, DAC 156 does not need to adjust the reference current (or only needs to make a minor adjustment), and thus in this case DAC 156 can be much smaller and simpler.

[0057] Although components are described in terms of functional limitations, it should be understood that a particular implementation necessarily includes the use of specific computing hardware. It should also be understood that in some embodiments, some of the components described herein include similar or common hardware. For example, in some embodiments, both sets of circuitry utilize the same (one or more) processors, (one or more) memories, (one or more) circuitry, and / or the like to perform their associated functions, such that each set of circuitry does not require duplicate hardware.

[0058] Reference will now be made to Figure 4 , which provides a flowchart illustrating example steps, processes, procedures, and / or operations in accordance with various embodiments of the present disclosure. The various methods described herein include, for example, as​Figure 4 The example methods shown herein can provide various technical benefits and improvements. Note that each block of the flowchart and combinations of blocks in the flowchart can be implemented by various components, such as hardware, firmware, circuitry, and / or other devices associated with the execution of software including one or more computer program instructions. For example, Figure 4 one or more of the processes described herein can be implemented by computer program instructions that can be stored in a non-transitory memory of a device adopting embodiments of the present disclosure and executed by a processor in the device. These computer program instructions can direct a computer or other programmable device to operate in a specific manner, such that the instructions stored in a computer-readable storage device memory produce a manufacture, the execution of which implements the functions specified in one or more of the flowchart blocks.

[0059] As described above and as will be appreciated based on the present disclosure, embodiments of the present disclosure can be configured as methods, mobile devices, backend network devices, etc. Thus, the embodiments can include a variety of means including entirely hardware or any combination of software and hardware. Additionally, embodiments can take the form of a computer program product on at least one non-transitory computer-readable storage medium having computer-readable program instructions (e.g., computer software) implemented in the storage medium. Similarly, embodiments can take the form of computer program code stored on at least one non-transitory computer-readable storage medium. Any suitable computer-readable storage medium can be utilized, including non-transitory hard disks, CD-ROMs, flash memory, optical storage devices, or magnetic storage devices.

[0060] Example systems, devices, computing environments, and user interfaces associated with embodiments of the present disclosure have been described. Now, an example flowchart including various operations performed by the circuits, devices, systems, and / or apparatuses described herein will be discussed. It should be recognized that each flowchart illustrates an example process that can be performed by one or more of the circuits, devices, systems, and / or apparatuses described herein (e.g., using one or more of its components). As shown and described herein, the blocks indicating the operations of each process can be arranged in any of a variety of ways. In some such embodiments, one or more blocks of any process described herein occur simultaneously rather than sequentially. In some such embodiments, one or more blocks of any process described herein occur between one or more blocks of another process, before one or more blocks of another process, and / or otherwise as a sub-process operation of a second process. Additionally or alternatively, any process can include some or all of the steps described and / or illustrated, including one or more optional operation blocks in some embodiments. With respect to the following flowcharts, in some or all embodiments of the present disclosure, one or more of the blocks shown can be optional. Optional blocks are drawn with a dashed line (or "dash"). Similarly, it should be recognized that one or more operations in each flowchart can be combined, replaced, reordered, and / or otherwise changed as described herein.

[0061] Now referring to Figure 4 , an example flowchart of an example method 400 for providing a reference current to a numerically controlled oscillator in accordance with some embodiments of the present disclosure is illustrated. In some embodiments, the example method 400 can be implemented by the example circuits described herein (including but not limited to the example circuit 100 described above in connection with Figure 1 .

[0062] In the Figure 4 example method shown, the example method 400 begins at step / operation 402. At step / operation 402, one or more components of the circuit (such as but not limited to the reference circuit portion 102 of the circuit 100 described above in connection with Figure 1 provide an input voltage or input current to a first input terminal of a differential circuit (such as but not limited to the differential circuit portion 122 described above in connection with Figure 1 .

[0063] At step / operation 404, one or more components of the circuit (such as but not limited to, the differential circuit portion 122 of the circuit 100 described above in connection with Figure 1 provide an output current to a replica CCO (such as but not limited to, the replica CCO 130 described above in connection with Figure 1 .

[0064] At step / operation 406, one or more components of the circuit, such as but not limited to the replicated CCO 130 of circuit 100 described above in conjunction with Figure 1 produce an output frequency.

[0065] At step / operation 408, one or more components of the circuit, such as but not limited to the frequency divider circuit portion 132 of circuit 100 described above in conjunction with Figure 1 divide the output frequency into a feedback frequency.

[0066] At step / operation 410, one or more components of the circuit, such as but not limited to the circuit 100 described above in conjunction with Figure 1 provide the feedback frequency to a switched capacitor resistor circuit, such as but not limited to the feedback switched capacitor resistor circuit 134 of circuit 100 described above in conjunction with Figure 1 At step / operation 412, one or more components of the circuit, such as but not limited to the feedback switched capacitor resistor circuit 134 of circuit 100 described above in conjunction with

[0067] provide a feedback voltage or feedback current to a second input of a differential circuit, such as but not limited to the differential circuit portion 122 of circuit 100 described above in conjunction with Figure 1 Figure 1 At step / operation 414, one or more components of the circuit, such as but not limited to the differential circuit portion 122 of circuit 100 described above in conjunction with adjust its output based on the difference between its input voltage and the feedback voltage or the difference between its input current and the feedback current.

[0068] At step / operation 416, one or more components of the circuit, such as but not limited to the differential circuit portion 122 of circuit 100 described above in conjunction with Figure 1 provide its output current as a reference current to a DCO, such as but not limited to the DCO 150 described above in conjunction with

[0069] In some embodiments, Figure 1 the example method shown in Figure 1 continues to repeat.

[0070] In some embodiments, Figure 4 the example method shown in

[0071] While the above description and the various figures mainly relate to providing a reference current to a DCO, embodiments of the present disclosure can also be used to provide a reference current to a VCO having a CCO. Such embodiments can be used to reduce the gain of the VCO in a charge pump PLL. One scheme used for a PLL is to have a charge pump and an analog loop filter provide a control voltage to a VCO having a voltage-to-current converter and a CCO. In various embodiments of the present invention, a replicated CCO (such as replicated CCO 130 of example circuit 100, replicated CCO 230 of example circuit 200, or replicated CCO 330 of example circuit 300) has performance that substantially matches that of the CCO of the VCO, and the generated reference current (such as reference current 160 from example circuit 100, reference current 260 from example circuit 200, or reference current 360 from example circuit 300) is provided to a second voltage-to-current converter of the VCO and the CCO of the VCO.

[0072] In various embodiments, an example circuit for providing a reference current to a DCO or a VCO can be modified to be used as a standalone analog frequency-locked loop (FLL). In such an embodiment, the output from the replicated CCO (in such an embodiment, it is not a replica because there is no other device having a replicated CCO) is provided not only to a frequency divider circuit portion (such as frequency divider circuit portion 132 of example circuit 100, frequency divider circuit portion 232 of example circuit 200, or frequency divider circuit portion 332 of example circuit 300), but also output from the example circuit to be used as a standalone analog FLL. This can operate as a standalone analog FLL (although a somewhat crude FLL) because the output from the "replicated" CCO is equal to N x f DIV , which is approximately equal to N x f REF .

[0073] Conclusion

[0074] Those skilled in the art will envision many modifications and other embodiments of the disclosure described herein after benefiting from the above description and the teachings presented in the associated drawings. While the various figures only show certain components of the devices and systems described herein, it should be understood that many other components can be used in conjunction with the systems. Accordingly, it should be understood that the present disclosure is not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. Additionally, the steps in the above methods do not necessarily occur in the order shown in the figures, and in some cases, one or more of the steps shown can occur substantially simultaneously or can involve additional steps. While specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0075] Although various embodiments in accordance with the principles disclosed herein have been shown and described above, those skilled in the art may make modifications thereto without departing from the spirit and teachings of the disclosure. The embodiments described herein are merely representative and are not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of the disclosure. The disclosed embodiments relate primarily to a fragmented wideband tympanometry technique for true wireless stereo, however, those skilled in the art will recognize that these principles may be applied to any audio device. Alternative embodiments resulting from combining, integrating, and / or omitting features of (one or more) embodiments are also within the scope of the disclosure. Accordingly, the scope of protection is not limited by the above description.

[0076] In addition, the section headings used herein are for consistency with the recommendations of 37 C.F.R. 1.77 or to otherwise provide organizational cues. These headings should not limit or characterize the disclosure(s) listed in any claim(s) that may issue from this disclosure.

[0077] Although this detailed description has set forth some embodiments of the disclosure, the appended claims cover other embodiments of the disclosure that differ from the described embodiments in various modifications and improvements. For example, the appended claims may cover any form of integrated circuit having one or more phase-locked loops or frequency-locked loops.

[0078] Within the appended claims, unless a specific term "means for... " or "step for... " is used in a given claim, the claim is not intended to be construed under paragraph 6 of 35 U.S.C. 112.

Claims

1. A circuit for providing a reference current to a device having a first current controlled oscillator (CCO), the circuit comprising: A reference circuit for providing an input voltage or an input current based on a reference frequency; as well as Feedback loop circuit, including: A differential circuit having a first input terminal, receiving an input voltage or an input current from a reference circuit and providing an output current; a second CCO receiving the output current from the differential circuit and generating an output frequency in response, the second CCO being adapted to have substantially matched performance to the first CCO; A frequency divider circuit for dividing the output frequency into a feedback frequency; and a feedback switched capacitor resistor circuit providing a feedback voltage or a feedback current to a second input terminal of the differential circuit based on a feedback frequency; wherein the differential circuit adjusts its output current based on a difference between an input voltage and a feedback voltage or a difference between an input current and a feedback current; wherein the differential circuit is adapted to provide an output current as a reference current to a device having a first CCO; and Wherein, since the second CCO has performance that substantially matches that of the first CCO, the feedback frequency is adapted to be substantially equal to a divided-down version of the output frequency of the device having the first CCO.

2. The circuit of claim 1, wherein the device having the first CCO comprises a digitally controlled oscillator (DCO) or a voltage controlled oscillator (VCO).

3. The circuit of claim 1, wherein the frequency divider circuit is selected such that the feedback frequency is equal to the reference frequency when the input voltage is equal to the feedback voltage or the input current is equal to the feedback current.

4. The circuit of claim 1, wherein the second CCO is adapted to have substantially the same structure as the first CCO.

5. The circuit of claim 1, wherein the differential circuit comprises a differential amplifier and a voltage-to-current converter connected to an output terminal of the differential amplifier.

6. The circuit of claim 1, wherein the reference circuit comprises a reference switched capacitor resistor circuit.

7. The circuit of claim 6, wherein the input voltage provided to the first input terminal of the differential circuit is a reference voltage; Wherein the reference circuit further comprises a differential amplifier and a voltage-to-current converter connected to the output terminal of the differential amplifier; wherein a reference voltage is provided to a first input terminal of the differential amplifier; wherein a reference frequency and a first current from a voltage-to-current converter are input to a reference switched capacitor resistor circuit to generate a first voltage provided to a second input terminal of the differential amplifier; wherein a first current from a voltage-to-current converter is mirrored to a feedback loop circuit to provide a second current; as well as The second current and the feedback frequency are input to a feedback switch capacitor resistor circuit to generate a feedback voltage provided to the differential circuit.

8. The circuit of claim 6, wherein the reference frequency and the first current are input to a reference switched capacitor resistor circuit to generate an input voltage provided to the first input terminal of the differential circuit; and The feedback frequency and a second current equal to the first current are input to the feedback switch capacitor resistor circuit to generate a feedback voltage provided to the second input terminal of the differential circuit.

9. The circuit of claim 6, wherein the reference circuit further comprises a first differential amplifier and a first voltage-to-current converter connected to an output terminal of the first differential amplifier; wherein a reference voltage is provided to a first input terminal of the first differential amplifier; wherein a reference frequency and a first current from a first voltage-to-current converter are input to a reference switched capacitor resistor circuit to generate a first voltage provided to a second input terminal of the first differential amplifier; wherein the first current from the first voltage-to-current converter is an input current provided to the first input terminal of the differential circuit; wherein the feedback loop circuit further comprises a second differential amplifier and a second voltage-to-current converter connected to the output terminal of the second differential amplifier; wherein a reference voltage is provided to a first input terminal of a second differential amplifier; wherein a second current from the second voltage-to-current converter is input to the feedback switched capacitor resistor circuit to generate a second voltage provided to a second input terminal of the second differential amplifier; as well as The second current from the second voltage-to-current converter is a feedback current to the second input terminal of the differential circuit.

10. A method of providing a reference current to a device having a first current controlled oscillator (CCO), the method comprising: The reference circuit provides an input voltage or an input current to a first input terminal of a differential circuit of the feedback loop circuit based on a reference frequency; The output current is provided by a differential circuit; receiving, by a second CCO, an output current from the differential circuit, the second CCO being adapted to have a performance substantially matched to the first CCO; generating an output frequency by a second CCO in response to the received output current; The output frequency is divided into the feedback frequency by the frequency divider circuit; providing a feedback voltage or a feedback current to a second input terminal of the differential circuit based on a feedback frequency by a feedback switched capacitor resistor circuit; The output current thereof is adjusted by a differential circuit based on a difference between an input voltage and a feedback voltage or a difference between an input current and a feedback current; The differential circuit provides an output current as a reference current to a device having a first CCO; Wherein, since the second CCO has performance that substantially matches that of the first CCO, the feedback frequency is adapted to be substantially equal to a divided-down version of the output frequency of the device having the first CCO.

11. The method of claim 10, wherein the device having the first CCO comprises a digitally controlled oscillator (DCO) or a voltage controlled oscillator (VCO).

12. The method of claim 10, wherein the frequency divider circuit is selected such that the feedback frequency is equal to the reference frequency when the input voltage is equal to the feedback voltage or the input current is equal to the feedback current.

13. The method of claim 10, wherein the second CCO is adapted to have substantially the same structure as the first CCO.

14. The method of claim 10, wherein the differential circuit comprises a differential amplifier and a voltage-to-current converter connected to an output terminal of the differential amplifier.

15. The method of claim 10, wherein the reference circuit comprises a reference switched capacitor resistor circuit.

16. The method of claim 15, wherein the input voltage provided to the first input terminal of the differential circuit is a reference voltage; The method further comprises: providing a reference voltage to a first input terminal of a differential amplifier of a reference circuit; providing a reference frequency and a first current from a voltage-to-current converter connected to an output terminal of the differential amplifier to a reference switched capacitor resistor circuit to generate a first voltage; providing a first voltage to a second input terminal of the differential amplifier; mirroring a first current from the voltage-to-current converter to a feedback loop circuit to provide a second current; and The second current and the feedback frequency are provided to a feedback switched capacitor resistor circuit to generate a feedback voltage that is provided to the differential circuit.

17. The method of claim 15, further comprising: providing a reference frequency and a first current to a reference switched capacitor resistor circuit to generate an input voltage provided to a first input terminal of a differential circuit; as well as A feedback frequency and a second current equal to the first current are provided to the feedback switched capacitor resistor circuit to generate a feedback voltage provided to the second input terminal of the differential circuit.

18. The method of claim 15, further comprising: providing a reference voltage to a first input terminal of a first differential amplifier of a reference circuit; providing a reference frequency and a first current from a first voltage-to-current converter connected to an output terminal of a first differential amplifier to a reference switched capacitor resistor circuit to generate a first voltage; providing a first voltage to a second input terminal of the first differential amplifier; providing a reference voltage to a first input terminal of a second differential amplifier of the feedback loop circuit; providing a second current from a second voltage-to-current converter connected to an output terminal of the second differential amplifier to the feedback switched capacitor resistor circuit to generate a second voltage; as well as providing a second voltage to a second input terminal of the second differential amplifier; wherein the first current from the first voltage-to-current converter is an input current provided to the first input terminal of the differential circuit; as well as The second current from the second voltage-to-current converter is a feedback current to the second input terminal of the differential circuit.

19. A circuit for providing a frequency output to be used as a frequency locked loop (FLL), the circuit comprising: A reference circuit for providing an input voltage or an input current based on a reference frequency; as well as Feedback loop circuit, including: A differential circuit having a first input terminal, receiving an input voltage or an input current from a reference circuit and providing an output current; a CCO that receives the output current from the differential circuit and generates an output frequency in response; A frequency divider circuit for dividing the output frequency into a feedback frequency; and a feedback switched capacitor resistor circuit providing a feedback voltage or a feedback current to a second input terminal of the differential circuit based on a feedback frequency; wherein the differential circuit adjusts its output current based on a difference between an input voltage and a feedback voltage or a difference between an input current and a feedback current; Therein the CCO is adapted to output an output frequency to be used as an FLL.

20. The circuit of claim 1, wherein the frequency divider circuit is selected such that the feedback frequency is equal to the reference frequency when the input voltage is equal to the feedback voltage or the input current is equal to the feedback current.

21. The circuit of claim 1, wherein the differential circuit comprises a differential amplifier and a voltage-to-current converter connected to an output of the differential amplifier.

22. The circuit of claim 1, wherein the reference circuit comprises a reference switched capacitor resistor circuit.

23. The circuit of claim 4, wherein the input voltage provided to the first input terminal of the differential circuit is a reference voltage; Wherein the reference circuit further comprises a differential amplifier and a voltage-to-current converter connected to the output terminal of the differential amplifier; wherein a reference voltage is provided to a first input terminal of the differential amplifier; wherein a reference frequency and a first current from a voltage-to-current converter are input to a reference switched capacitor resistor circuit to generate a first voltage provided to a second input terminal of the differential amplifier; wherein a first current from a voltage-to-current converter is mirrored to a feedback loop circuit to provide a second current; as well as The second current and the feedback frequency are input to a feedback switch capacitor resistor circuit to generate a feedback voltage provided to the differential circuit.

24. The circuit of claim 4, wherein the reference frequency and the first current are input to a reference switched capacitor resistor circuit to generate an input voltage provided to the first input terminal of the differential circuit; and The feedback frequency and a second current equal to the first current are input to the feedback switch capacitor resistor circuit to generate a feedback voltage provided to the second input terminal of the differential circuit.

25. The circuit of claim 4, wherein the reference circuit further comprises a first differential amplifier and a first voltage-to-current converter connected to an output terminal of the first differential amplifier; wherein a reference voltage is provided to a first input terminal of the first differential amplifier; wherein a reference frequency and a first current from a first voltage-to-current converter are input to a reference switched capacitor resistor circuit to generate a first voltage provided to a second input terminal of the first differential amplifier; wherein the first current from the first voltage-to-current converter is an input current provided to the first input terminal of the differential circuit; wherein the feedback loop circuit further comprises a second differential amplifier and a second voltage-to-current converter connected to the output terminal of the second differential amplifier; wherein a reference voltage is provided to a first input terminal of a second differential amplifier; wherein a second current from the second voltage-to-current converter is input to the feedback switched capacitor resistor circuit to generate a second voltage provided to a second input terminal of the second differential amplifier; as well as The second current from the second voltage-to-current converter is a feedback current to the second input terminal of the differential circuit.

26. A method of providing a frequency output to be used as a frequency locked loop (FLL), the method comprising: The reference circuit provides an input voltage or an input current to a first input terminal of a differential circuit of the feedback loop circuit based on a reference frequency; The output current is provided by a differential circuit; The CCO receives the output current from the differential circuit; generating an output frequency by the CCO in response to the received output current; The output frequency is divided into the feedback frequency by the frequency divider circuit; providing a feedback voltage or a feedback current to a second input terminal of the differential circuit based on a feedback frequency by a feedback switched capacitor resistor circuit; The output current thereof is adjusted by a differential circuit based on a difference between an input voltage and a feedback voltage or a difference between an input current and a feedback current; The CCO outputs the frequency to be used as the output frequency of the FLL.

27. The method of claim 8, wherein the divider circuit is selected such that the feedback frequency is equal to the reference frequency when the input voltage is equal to the feedback voltage or the input current is equal to the feedback current.

28. The method of claim 8, wherein the differential circuit comprises a differential amplifier and a voltage-to-current converter connected to an output terminal of the differential amplifier.

29. The method of claim 8, wherein the reference circuit comprises a reference switched capacitor resistor circuit.

30. The method of claim 11, wherein the input voltage provided to the first input terminal of the differential circuit is a reference voltage; The method further comprises: providing a reference voltage to a first input terminal of a differential amplifier of a reference circuit; providing a reference frequency and a first current from a voltage-to-current converter connected to an output terminal of the differential amplifier to a reference switched capacitor resistor circuit to generate a first voltage; providing a first voltage to a second input terminal of the differential amplifier; mirroring a first current from the voltage-to-current converter to a feedback loop circuit to provide a second current; and The second current and the feedback frequency are provided to a feedback switched capacitor resistor circuit to generate a feedback voltage that is provided to the differential circuit.

31. The method of claim 11, further comprising: providing a reference frequency and a first current to a reference switched capacitor resistor circuit to generate an input voltage provided to a first input terminal of a differential circuit; as well as A feedback frequency and a second current equal to the first current are provided to the feedback switched capacitor resistor circuit to generate a feedback voltage provided to the second input terminal of the differential circuit.

32. The method of claim 11, further comprising: providing a reference voltage to a first input terminal of a first differential amplifier of a reference circuit; providing a reference frequency and a first current from a first voltage-to-current converter connected to an output terminal of a first differential amplifier to a reference switched capacitor resistor circuit to generate a first voltage; providing a first voltage to a second input terminal of the first differential amplifier; providing a reference voltage to a first input terminal of a second differential amplifier of the feedback loop circuit; providing a second current from a second voltage-to-current converter connected to an output terminal of the second differential amplifier to the feedback switched capacitor resistor circuit to generate a second voltage; as well as providing a second voltage to a second input terminal of the second differential amplifier; wherein the first current from the first voltage-to-current converter is an input current provided to the first input terminal of the differential circuit; as well as The second current from the second voltage-to-current converter is a feedback current to the second input terminal of the differential circuit.

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