Differential switching output stage for audio, power and digital data transmission can cause a common mode error due to asymmetric transition between positive and negative outputs. Systems and methods are provided for common mode error correction. In particular, summing nodes, novel error amps an edge switching can be used for common-mode feedback (CMFB) in differential signaling and other applications.

This application provides an operational amplifier and a start-up circuit of the operational amplifier. The start-up circuit has advantages of simple structure and low power consumption. The operational amplifier includes a multi-stage amplifier and a start-up circuit, where the start-up circuit includes: a first start-up transistor M16 and a second start-up transistor M17, a source of the first start-up transistor M16 and a source of the second start-up transistor M17 are connected to a tail bias node of a first-stage amplifier in the multi-stage amplifier, a gate of the first start-up transistor M16 and a gate of the second start-up transistor M17 are configured to connect to a first bias voltage V.sub.b, and a drain of the first start-up transistor M16 and a drain of the second start-up transistor M17 are connected to input terminals of a second-stage or higher-stage amplifier.

A low energy transmitter is provided. The transmitter includes an antenna circuit wherein the antenna circuit has an antenna positive node interface (Vop) and an antenna negative node interface (Von); a reference voltage source that supplies a reference voltage to the antenna circuit; and a common mode feedback (CMFB) circuit coupled to the antenna circuit that receives from the antenna circuit inputs from the Vop and the Von and supplies at least one signal to the antenna circuit.

A signal receiving device includes a first amplifier, a duty cycle adjuster and a common mode feedback circuit. The first amplifier receives an input signal, a reference voltage and a bias voltage. The first amplifier generates a first common current based on the bias voltage and, based on the first common current, generates a first output signal and a second output signal complementary to each other by comparing the input signal and the reference voltage. The duty cycle adjuster charges and discharges a selected capacitor according to the first output signal or the second output signal to generate a sensing voltage, and generates a common reference voltage according to the sensing voltage. The common mode feedback circuit generates the bias voltage by comparing the common reference voltage and the reference voltage.

A low energy transmitter is provided. The transmitter includes an antenna circuit wherein the antenna circuit has an antenna positive node interface (Vop) and an antenna negative node interface (Von); a reference voltage source that supplies a reference voltage to the antenna circuit; and a common mode feedback (CMFB) circuit coupled to the antenna circuit that receives from the antenna circuit inputs from the Vop and the Von and supplies at least one signal to the antenna circuit.

An amplifying circuit may include: an amplifier configured to receive a first input voltage and output a first output voltage by amplifying the first input voltage; and a common-mode feedback circuit configured to enable the first output voltage to operate in a common mode by receiving the first output voltage and performing a feedback to adjust at least one feedback voltage applied to the amplifier based on the first output voltage. The common-mode feedback circuit may include a first Miller compensation circuit configured to perform dominant pole compensation by using a Miller effect for the common-mode feedback circuit. The first Miller compensation circuit may include a resistor and a capacitor.

Disclosed include methods and devices for enabling a battery free Bluetooth low energy communication. Some embodiments include a transmitter and a reference voltage generator supplying a voltage to an oscillator circuit. Further, some embodiments include an oscillator circuit including two pairs of semiconductor devices, wherein each pair of a semiconductor device includes a device with a gate node coupled to an antenna positive node interface (Vop) via a capacitor and a drain connected to an antenna negative node interface (Von) and a device with a gate node coupled to an antenna positive node interface (Von) via a capacitor and a drain connected to an antenna negative node interface (Vop). Additionally, some embodiments include an oscillator circuit connected to a common mode feedback circuit.

Disclosed include methods and devices for enabling a battery free Bluetooth low energy communication. Some embodiments include a transmitter and a reference voltage generator supplying a voltage to an oscillator circuit. Further, some embodiments include an oscillator circuit including two pairs of semiconductor devices, wherein each pair of a semiconductor device includes a device with a gate node coupled to an antenna positive node interface (Vop) via a capacitor and a drain connected to an antenna negative node interface (Von) and a device with a gate node coupled to an antenna positive node interface (Von) via a capacitor and a drain connected to an antenna negative node interface (Vop). Additionally, some embodiments include an oscillator circuit connected to a common mode feedback circuit.

An amplifying circuit may include: an amplifier configured to receive a first input voltage and output a first output voltage by amplifying the first input voltage; and a common-mode feedback circuit configured to enable the first output voltage to operate in a common mode by receiving the first output voltage and performing a feedback to adjust at least one feedback voltage applied to the amplifier based on the first output voltage. The common-mode feedback circuit may include a first Miller compensation circuit configured to perform dominant pole compensation by using a Miller effect for the common-mode feedback circuit. The first Miller compensation circuit may include a resistor and a capacitor.

Certain aspects of the present disclosure generally relate to a reconfigurable active filter and techniques for using such a filter. One example reconfigurable active filter may include an amplifier including: a first input stage coupled between an input of the amplifier and an output of the amplifier, and a second input stage selectively coupled between the input of the amplifier and the output of the amplifier. The reconfigurable active filter may also include at least two feedback paths selectively coupled between the input of the amplifier and the output of the amplifier.