A coupling module can be used to communicate high speed signals between an optical transceiver and a processing module of an optical communication device, such as an optical line termination (OLT) or an optical network unit (ONU). The coupling module can adjust the common mode voltage level of a differential signal output by the optical transceiver to the common mode voltage level required by the processing module. In addition, the coupling module splits each of the differential output signals from the optical transceiver and passes the split signals to both a high-pass filter and a low-pass filter that are connected in parallel. The outputs of the high-pass filter and the low-pass filter from different paths of the differential signal are cross-coupled and combined to provide a differential signal to the processing module.

A coupling module can be used to communicate high speed signals between an optical transceiver and a processing module of an optical communication device, such as an optical line termination (OLT) or an optical network unit (ONU). The coupling module can adjust the common mode voltage level of a differential signal output by the optical transceiver to the common mode voltage level required by the processing module. In addition, the coupling module splits each of the differential output signals from the optical transceiver and passes the split signals to both a high-pass filter and a low-pass filter that are connected in parallel. The outputs of the high-pass filter and the low-pass filter from different paths of the differential signal are cross-coupled and combined to provide a differential signal to the processing module.

A tunable filter is described where the frequency response as well as bandwidth and transmission loss characteristics can be dynamically altered, providing improved performance for transceiver front-end tuning applications. The rate of roll-off of the frequency response can be adjusted to improve performance when used in duplexer applications. The tunable filter topology is applicable for both transmit and receive circuits. A method is described where the filter characteristics are adjusted to account for and compensate for the frequency response of the antenna used in a communication system.

In some examples, a circuit includes an amplifier, a resistor, and a damping network. The amplifier has an amplifier output and first and second amplifier inputs. The first amplifier input is adapted to be coupled to a first terminal, and the second amplifier input is configured to receive a reference voltage. The resistor is coupled between the amplifier output and the first amplifier input. The damping network is coupled between the amplifier output and the first terminal.

An apparatus is disclosed for a harmonic rejection filter with transimpedance amplifiers. In an example aspect, the apparatus includes a harmonic rejection filter with at least three input nodes, at least one output node, a first transimpedance amplifier, a first set of transimpedance amplifiers, and a scaling current converter. The at least three input nodes include a first input node, a second input node, and a third input node. The at least one output node includes a first output node. The first transimpedance amplifier is coupled between the first input node and the first output node. The first set of transimpedance amplifiers include a second transimpedance amplifier coupled to the second input node and a third transimpedance amplifier coupled to the third input node. The scaling current converter is coupled between outputs associated with the first set of transimpedance amplifiers and an input of the first transimpedance amplifier.

An apparatus is disclosed for a harmonic rejection filter with transimpedance amplifiers. In an example aspect, the apparatus includes a harmonic rejection filter with at least three input nodes, at least one output node, a first transimpedance amplifier, a first set of transimpedance amplifiers, and a scaling current converter. The at least three input nodes include a first input node, a second input node, and a third input node. The at least one output node includes a first output node. The first transimpedance amplifier is coupled between the first input node and the first output node. The first set of transimpedance amplifiers include a second transimpedance amplifier coupled to the second input node and a third transimpedance amplifier coupled to the third input node. The scaling current converter is coupled between outputs associated with the first set of transimpedance amplifiers and an input of the first transimpedance amplifier.

An audio filter and corresponding method with through-zero linearly variable resonant frequency are described. An example method includes receiving an input signal; receiving one or more control input signals; and providing a resonant filter for electronic music for processing the input signal. The resonant filter can include an exponential times linear multiplication to produce the resonant frequency control responsive to control voltages exponentially for musical octave/semitone control, and linearly for timbre modulation, the waveform being invariant over corresponding exponential changes in pitch of both input signal and filter resonance. The linear modulation can include inverting the sign of a bandpass feedback based on the sign of the resonant frequency variable so as to maintain stability. In the example method, to prevent a glitch on the output when frequency changes sign, a separate highpass output signal may be generated.

A tunable filter is described where the frequency response as well as bandwidth and transmission loss characteristics can be dynamically altered, providing improved performance for transceiver front-end tuning applications. The rate of roll-off of the frequency response can be adjusted to improve performance when used in duplexer applications. The tunable filter topology is applicable for both transmit and receive circuits. A method is described where the filter characteristics are adjusted to account for and compensate for the frequency response of the antenna used in a communication system.

The embodiments of the present disclosure provide a method and system for adjusting a passband width of a filter. The method includes determining an initial passband width, controlling a filter according to the initial passband width to filter signals to be processed, and correcting the initial passband width according to a first frequency at which a peak spectrum line corresponding to the filtered signals is located.

An aspect includes a filtering method including operating a first filter to filter a first input signal to generate a first output signal; operating a second filter to filter a second input signal to generate a second output signal; and selectively coupling at least a portion of the second filter with the first filter to filter a third input signal to generate a third output signal. Another aspect includes a filtering method including operating switching devices to configure a filter with a first set of pole(s); filtering a first input signal to generate a first output signal with the filter configured with the first set of pole(s); operating the switching devices to configure the filter with a second set of poles; and filtering a second input signal to generate a second output signal with the filter configured with the second set of poles.