Receiver system

A filter circuit including an equivalent inductor circuit, wherein the equivalent inductor circuit comprises:

• a capacitor;
• a gyrator composed of a plurality of operational transconductance amplifiers and having said capacitor as a load;
• and
• a resistor connected in series with said capacitor.

An adjustment-free filter circuit comprising:

• a first filter circuit including an equivalent inductor circuit comprising a first capacitor, a gyrator composed of a plurality of operational transconductance amplifiers and having said first capacitor as a load, and a resistor connected in series with said first capacitor, said first filter circuit receiving a signal having a predetermined frequency;
• a phase comparator circuit for producing a signal commensurate with a phase difference between said signal having the predetermined frequency and an output signal of said first filter circuit;
• a second filter circuit including an equivalent inductor circuit comprising a second capacitor, a gyrator composed of a plurality of operational transconductance amplifiers and having said second capacitor as a load, and a resistor connected in series with said second capacitor;
• and
• a control circuit for varying, according to an output signal of said phase comparator circuit, currents produced by current sources provided in the operational transconductance amplifiers provided in said first and second filter circuits.

A receiver system including a filter circuit including an equivalent inductor circuit, wherein the equivalent inductor circuit comprises:

• a capacitor;
• a gyrator composed of a plurality of operational transconductance amplifiers and having said capacitor as a load;
• and
• a resistor connected in series with said capacitor.

A receiver system including an adjustment-free filter circuit, wherein the adjustment-free filter circuit comprises:

• a first filter circuit including an equivalent inductor circuit comprising a first capacitor, a gyrator composed of a plurality of operational transconductance amplifiers and having said first capacitor as a load, and a resistor connected in series with said first capacitor, said first filter circuit receiving a signal having a predetermined frequency;
• a phase comparator circuit for producing a signal commensurate with a phase difference between said signal having the predetermined frequency and an output signal of said first filter circuit;
• a second filter circuit including an equivalent inductor circuit comprising a second capacitor, a gyrator composed of a plurality of operational transconductance amplifiers and having said second capacitor as a load, and a resistor connected in series with said second capacitor;
• and
• a control circuit for varying, according to an output signal of said phase comparator circuit, currents produced by current sources provided in the operational transconductance amplifiers provided in said first and second filter circuits.

A receiver system comprising:

• an antenna for receiving a high-frequency signal;
• an amplifier for amplifying the high-frequency signal output from said antenna;
• a local oscillator for producing a local oscillation signal;
• a mixer for mixing an output signal of said amplifier and the local oscillation signal to produce an intermediate signal;
• and
• a band-pass filter circuit for eliminating unnecessary frequency components from an output signal of said mixer,
• wherein said band-pass filter circuit is composed of a low-pass filter that receives the output signal of said mixer and a band-pass filter that receives an output signal of said low-pass filter,
• a value obtained by dividing a higher cutoff frequency of said band-pass filter by a lower cutoff frequency thereof is smaller than 2, and a cutoff frequency of said low-pass filter is higher than a center frequency of said band-pass filter.