Low power radio telephone image reject mixer
AssigneeInternational Business Machines Corporation
InventorJean-Marc Mourant
Life of this patent
Estimating the term…
Abstract
An image reject mixer for a low power battery operated radio telephone application. First and second doubly balance mixer circuits are connected to receive a differential radio frequency signal. Each of the doubly balance mixer circuits receives a local oscillator signal and a complimentary quadrature local oscillator signal. A first and second differential current produced by the first and second doubly balance mixture are combined in a quadrature combining circuit. The quadrature combining circuit adds an additional 90° of phase shift between the pairs of signals produced by each doubly balance mixture, so that the mixture output signals are added in a phase quadrature relationship thereby canceling unwanted spur and image components contained in the respective mixer output circuits.
Claims10
An image reject mixer comprising:
- first doubly balanced mixer receiving a local oscillator signal and an radio frequency signal, said doubly balanced mixer providing first and second differential currents which represent the sum and difference of said local oscillator signal and said radio frequency signal;
- a second doubly balanced mixer receiving said local oscillator signal which has been phase shifted, and said radio frequency signal said second doubly balanced mixer producing first and second differential currents which represent the sum and difference of said phase shifted local oscillator signal and said radio frequency signal;
- each of said doubly balanced mixers comprising first and second pairs of bipolar transistors, said first and second pairs of transistors receiving said local oscillator signal between respective base connections, said first pair of transistors having emitters connected through impedance elements to one side of a source of radio frequency signals, said second pair of transistors having emitters connected through impedance elements to a second side of said source of radio frequency signals, and collectors of said transistors of said first pair of transistors being connected to collectors of transistors of said second pair of transistors to provide said first and second differential currents;
- and
- a quadrature combiner circuit for combining said first and second doubly balanced mixer first and second differential currents in a substantially quadrature relationship, and producing a pair of differential I.F. signals which are substantially free of signal images.
An image reject mixer comprising:
- first and second doubly balanced mixers which produce first and second differential currents, said differential currents being phase shifted at substantially ninety degrees from each other, representing the difference between a local oscillator signal and an radio frequency signal;
- and
- a quadrature combiner which combines said first and second differential currents in a substantially quadrature relationship to produce an output differential current, comprising:
- first and second transistors having base connections connected to one end of first and second capacitors;
- and emitter connections connected through fist and second emitter resistors to a remaining end of a respective of said first and second capacitors to form a first input for said first differential current;
- third and fourth transistors having base connections connected at one end to third and fourth capacitors, a collector of said third transistor being connected to a collector of said first transistor, and a collector of said fourth transistor being connected to a collector of said second transistor, said third and fourth transistors having emitter connections connected through third and fourth emitter resistors to a remaining end of respective of said third and fourth capacitors to form a second input for said second differential current;
- a first phase shift impedance connected between said first and second transistors emitter connections;
- a second phase shift impedance connected between said third and fourth transistors emitter connections;
- a first load impedance connected to said collector of said first transistor and to a source of voltage potential;
- a second load impedance connected to said collector of said fourth transistor and to said source of voltage potential;
- said first transistor collector and said fourth transistor collector producing said output differential current.
Dependencies are inferred from the claim text.