Double balanced mixer circuit with active filter load for a portable comunication receiver

A mixer circuit comprising:

• a multiplication circuit having a first input suitable for connection to an oscillator signal and a second input suitable for connection to a radio frequency (RF) signal to be mixed with the oscillator signal, the multiplication circuit generating at first and second differential outputs an output current which is a multiplication of the oscillator signal and the RF signal;
• a direct-current (DC) current source coupled to the multiplication circuit for supplying DC current for operation of the multiplication circuit;
• an active filter circuit coupled to the multiplication circuit, the active filter circuit being biased for operation by DC current that is coupled to it through the output of the multiplication circuit from the DC current source, the active filter circuit comprising:
• a common-base amplifier coupled to the output of the multiplication circuit and generating a current output in response to the output current of the multiplication circuit, the common-base amplifier being a differential common-base amplifier comprising:
• a voltage bias;
• and
• first and second transistors each comprising an emitter, base and collector, the emitter of the first transistor coupled to the first differential output of the multiplication circuit and the emitter of the second transistor coupled to the second differential output of the multiplication circuit, the DC current being coupled to the active filter circuit through the emitters of the first and second transistors, and the bases of the first and second transistors being coupled to the voltage bias;
• and
• a low pass active filter coupled to the common-base amplifier for filtering the current output of the common-base amplifier and generating at an output a filtered mixer output signal.

A receiver circuit suitable for connection to an antenna for receiving a radio frequency (RF) signal detected by the antenna, the receiver circuit comprising:

• an amplifier for amplifying the RF signal detected by the antenna and generating an amplified RF signal;
• at least one local oscillator for generating a local oscillator signal;
• at least one mixer coupled to the at least one local oscillator and to an output of the amplifier, the at least one mixer comprising:
• a multiplication circuit having a first input coupled to the local oscillator signal and a second input coupled to the amplified RF signal, the multiplication circuit generating at an output an output current which is a multiplication of the local oscillator signal and the amplified RF signal;
• a direct-current (DC) current source coupled to the multiplication circuit for supplying DC current for operation of the multiplication circuit;
• an active filter circuit coupled to the multiplication circuit, the active filter circuit being biased for operation by DC current that is coupled to it through the output of the multiplication circuit from the DC current source, the active filter circuit comprising:
• a common-base amplifier coupled to the output of the multiplication circuit and generating a current output in response to the output current of the multiplication circuit, wherein the common-base amplifier comprises a voltage bias, a first transistor comprising an emitter, base and collector, the emitter of the first transistor coupled to the output of the multiplication circuit, the DC current being coupled to the active filter circuit through the emitter of the first transistor, and the base of the first transistor coupled to the voltage bias;
• a low pass active filter coupled to the common-base amplifier for filtering the current output of the common-base amplifier and generating at an output a filtered mixer output signal;
• and
• a demodulator coupled to an output of the at least one mixer for demodulating the filtered mixer output signal to generate a recovered audio signal.

A receiver circuit suitable for connection to an antenna for receiving a radio frequency (RF) signal detected by the antenna, the receiver circuit comprising:

• an amplifier for amplifying the RF signal detected by the antenna and generating an amplified RF signal;
• at least one local oscillator for generating a local oscillator signal;
• at least one mixer coupled to the at least one local oscillator and to an output of the amplifier, the at least one mixer comprising:
• a multiplication circuit having a first input coupled to the local oscillator signal and a second input coupled to the amplified RF signal, the multiplication circuit generating at first and second differential outputs an output current which is a multiplication of the local oscillator signal and the amplified RF signal;
• a direct-current (DC) current source coupled to the multiplication circuit for supplying DC current for operation of the multiplication circuit;
• an active filter circuit coupled to the multiplication circuit, the active filter circuit being biased for operation by DC current that is coupled to it through the output of the multiplication circuit from the DC current source, the active filter circuit comprising:
• a common-base amplifier coupled to the output of the multiplication circuit and generating a current output in response to the output current of the multiplication circuit, the common-base amplifier being a differential common-base amplifier comprising:
• a voltage bias;
• and
• first and second transistors each comprising an emitter, base and collector, the emitter of the first transistor coupled to the first differential output of the multiplication circuit and the emitter of the second transistor coupled to the second differential output of the multiplication circuit, the DC current being coupled to the active filter circuit through the emitters of the first and second transistors, and the bases of the first and second transistors being coupled to the voltage bias;
• a low pass active filter coupled to the common-base amplifier for filtering the current output of the common-base amplifier and generating at an output a filtered mixer output signal;
• and
• a demodulator coupled to an output of the at least one mixer for demodulating the filtered mixer output signal to generate a recovered audio signal.