Receiver system

Abstract

A receiver system includes an antenna to receive a high-frequency signal; a first band pass filter circuit to eliminate unnecessary frequency components from the high-frequency signal; a low-noise amplifier to amplify signal output from the first band pass filter circuit; a local oscillator to produce a local oscillation signal; a mixer to mix signal output from the low-noise amplifier and the local oscillation signal to produce an intermediate signal; a second band pass filter circuit to eliminate unnecessary frequency components from the intermediate signal; an amplifier to amplify signal output from the second band pass filter circuit; a demodulator circuit to demodulate signal output from the amplifier; an analog-to-digital converter circuit to convert signal output from the demodulator into digital signal.

1 . A receiver system comprising:
 an antenna to receive a high-frequency signal;   a first band pass filter circuit to eliminate unnecessary frequency components from the high-frequency signal;   a low-noise amplifier to amplify signal output from the first band pass filter circuit;   a local oscillator to produce a local oscillation signal;   a mixer to mix signal output from the low-noise amplifier and the local oscillation signal to produce an intermediate signal;   a second band pass filter circuit to eliminate unnecessary frequency components from the intermediate signal;   an amplifier to amplify signal output from the second band pass filter circuit;   a demodulator circuit to demodulate signal output from the amplifier;   an analog-to-digital converter circuit to convert signal output from the demodulator into digital signal.   
   
   
       2 . The receiver apparatus according to  claim 1 , wherein the second band pass filter circuit includes:
 a plurality of first filter circuits, each includes an equivalent inductor circuit comprising a first capacitor, a gyrator composed of a plurality of operational transconductance amplifiers and having the first capacitor as a load, and a resistor connected in series with said first capacitor;   a plurality of second filter circuits, each includes an equivalent inductor circuit comprising a second capacitor, a gyrator composed of a plurality of operational transconductance amplifiers and having the second capacitor as a load, and a resistor connected in series with the second capacitor;   a plurality of capacitors connected with the first and second filter circuits; and   an equivalent resistor circuit connected in parallel with the one of the second filter circuit, wherein an impedance of one of the first filter circuit and an impedance of one of the second filter circuit exclude negative resistance in a frequency band above 900 kHz.   
   
   
       3 . The receiver apparatus according to  claim 1 , further comprises:
 a phase control loop to automatically set a center frequency of the second band pass filter circuit, wherein the phase control loop includes:
 a reference clock source; 
 a frequency divider circuit; 
 a phase comparator circuit; 
 a low-pass filter circuit; 
 a charge pump circuit; 
 a loop filter, and 
 a control voltage generator circuit. 
   
   
   
       4 . The receiver apparatus according to  claim 3 , wherein the low-pass filter circuit includes an equivalent inductor circuit, a capacitor, and an equivalent resistor circuit connected in parallel with the capacitor, wherein the equivalent inductor circuit is composed of:
 a capacitor;   a gyrator composed of a plurality of operational transconductance amplifiers and having the capacitor as a load; and   a resistor connected in series with the capacitor.   
   
   
       5 . The receiver apparatus according to  claim 3 , wherein the control voltage generator circuit includes a variable current source and an NPN type transistor, the variable current source is connected to a collector of the NPN type transistor, an emitter of the NPN type transistor is grounded, the collector and a base of the NPN type transistor are connected together, wherein a constant voltage is supplied from a terminal to the variable current source.