An N-tap feedforward equalizer (FFE) comprises a set of N FFE taps coupled together in parallel, a filter coupled between the (N−1)th FFE tap and the Nth FFE tap, and a summer coupled to an output of the set of N FFE taps. Each FFE tap includes a unique sample-an-hold (S/H) circuit that generates a unique time-delayed signal and a unique transconductance stage that generates a unique transconductance output based on the unique time-delayed signal. The filter causes the N-tap FFE to have the behavior of greater than N taps. In some examples, the filter is a first order high pass filter that causes coefficients greater than N to have an opposite polarity of the Nth coefficient. In some examples, the filter is a first order low pass filter that causes coefficients greater than N to have the same polarity as the Nth coefficient.

An example apparatus includes a polyphase transconductance-capacitor filter. The polyphase filter includes a DC bias voltage node, a plus in-phase filter unit, a minus in-phase filter unit, a plus quadrature-phase filter unit, and a minus quadrature-phase filter unit. Each filter unit respectively includes an input node, an output node, and a control node. The polyphase filter also includes a plus in-phase switch and a minus in-phase switch. The plus in-phase switch is coupled to the control node of the plus in-phase filter unit, the DC bias voltage node, and the input node of one or both of the plus quadrature-phase filter unit and the minus quadrature-phase filter unit. The minus in-phase switch is coupled to the control node of the minus in-phase filter unit, the DC bias voltage node, and the input node of one or both of the plus quadrature-phase filter unit and the minus quadrature-phase filter unit.

An example apparatus includes a polyphase transconductance-capacitor filter. The polyphase filter includes a DC bias voltage node, a plus in-phase filter unit, a minus in-phase filter unit, a plus quadrature-phase filter unit, and a minus quadrature-phase filter unit. Each filter unit respectively includes an input node, an output node, and a control node. The polyphase filter also includes a plus in-phase switch and a minus in-phase switch. The plus in-phase switch is coupled to the control node of the plus in-phase filter unit, the DC bias voltage node, and the input node of one or both of the plus quadrature-phase filter unit and the minus quadrature-phase filter unit. The minus in-phase switch is coupled to the control node of the minus in-phase filter unit, the DC bias voltage node, and the input node of one or both of the plus quadrature-phase filter unit and the minus quadrature-phase filter unit.

An active high gain filter includes high value resistances in feedback implemented using a negative resistance circuit configuration. The high value resistance is implemented using two or smaller resistances connected in the negative resistance circuit configuration. This implementation permits integration of the filter circuit using less occupied area while still providing an accurate transfer function response.

An N-tap feedforward equalizer (FFE) comprises a set of N FFE taps coupled together in parallel, a filter coupled between the (N−1)th FFE tap and the Nth FFE tap, and a summer coupled to an output of the set of N FFE taps. Each FFE tap includes a unique sample-an-hold (S/H) circuit that generates a unique time-delayed signal and a unique transconductance stage that generates a unique transconductance output based on the unique time-delayed signal. The filter causes the N-tap FFE to have the behavior of greater than N taps. In some examples, the filter is a first order high pass filter that causes coefficients greater than N to have an opposite polarity of the Nth coefficient. In some examples, the filter is a first order low pass filter that causes coefficients greater than N to have the same polarity as the Nth coefficient.

A filter circuit comprising: a signal path for carrying a signal from an input to an output; the signal path comprising a first reactive component; a first node on the signal path; a first series resonant circuit comprising at least a second reactive component in series with a third reactive component, the first series resonant circuit being connected between the first node and a ground; an active circuit; the active circuit comprising a voltage controlled current source (VCCS) arranged to change the current flow through the second reactive component in dependence on a voltage sensed (or measured) on the signal path. The first series resonant circuit forms a single harmonic trap with a notch frequency defined by the component values of its reactive components. The effectiveness of the series resonant circuit is dependent upon the strength with which it draws current from the signal path at its resonant frequency.

Systems and methods for improving source-follower-based Sallen-Key architectures are disclosed. In particular, systems and methods for circumventing the non-idealities associated with source-follower-based Sallen-Key biquad filters when used in either baseband signal or radiofrequency paths. The systems and methods disclosed herein present power-efficient, cost-efficient solutions that can be implemented in a reduced area of a circuit.

An apparatus is disclosed for current-mode filtering using current steering. In an example aspect, the apparatus includes a filter. The filter includes a current-steering node, a first output node, a second output node, a wideband path, and a narrowband path. The wideband path is coupled between the current-steering node and the first output node. The wideband path includes a wideband low-pass filter configured to pass frequencies within a wide passband. The narrowband path is coupled between the current-steering node and the second output node. The narrowband path includes a narrowband low-pass filter configured to pass a portion of the frequencies that are within a narrow passband.

An apparatus is disclosed for current-mode filtering using current steering. In an example aspect, the apparatus includes a filter. The filter includes a current-steering node, a first output node, a second output node, a wideband path, and a narrowband path. The wideband path is coupled between the current-steering node and the first output node. The wideband path includes a wideband low-pass filter configured to pass frequencies within a wide passband. The narrowband path is coupled between the current-steering node and the second output node. The narrowband path includes a narrowband low-pass filter configured to pass a portion of the frequencies that are within a narrow passband.

A reconfigurable filter circuit has a first path including a transimpedance amplifier (TIA). The transimpedance amplifier has an input that receives an input current and an output that outputs a voltage. The reconfigurable filter circuit also includes a switchable feedback path. The switchable feedback path includes a first low-pass filter coupled to an output of the TIA. The switchable feedback path also includes a first switch to couple the feedback path to provide a feedback current to the first path resulting in a bandpass response in the output voltage when the switch is closed and a low-pass response in the output voltage when the switch is open.