Circuit and method for receiving and mixing radio frequencies in a direct conversion receiver

Abstract

A frequency mixing circuit and a frequency mixing method. The frequency mixing circuit includes first and second differential amplifiers, a subtracter and a mixer. The first differential amplifier amplifies a first pair of input signals having a first frequency to generate a first differential signal. The second differential amplifier amplifies a second pair of input signals having the first frequency orthogonal to the first pair input signals to generate a second differential signal. The subtracter subtracts the second differential signal from the first differential signal. The mixer mixes the subtracted signal with a first and second pairs of drive signals having a second frequency orthogonal to each other, in a sub-harmonic double balanced mixing mode, so that the mixer generates a pair of output signals orthogonal to each other without secondary harmonics.

1 . A circuit for receiving a radio frequency signal comprising: 
 a first poly-phase filter for transforming a radio frequency signal having a first frequency(f 1 ) into two pairs of input signals orthogonal to each other;    a second poly-phase filter for transforming a local oscillator signal into a first and second signals groups being 45° out of phase with respect to each other, each of the signal groups having two pairs of drive signals orthogonal to each other;    a first mixer for mixing the two pairs of input signals and the two pairs of drive signals in the first signal group and for outputting a first output signal having a third frequency, the first mixer being operatively connected to the first and second poly-phase filters; and    a second mixer for mixing the two pairs of input signals and the two pairs of drive signals in the second signal group and for outputting a second output signal having a substantially same frequency as the third frequency, the second mixer being operatively connected to the first and second poly-phase filters.    
   
   
       2 . The circuit of  claim 1 , wherein the first and second output signals are orthogonal to each other.  
   
   
       3 . The circuit of  claim 1 , wherein each of the first and second mixers is a sub-harmonic double balanced mixer adapted to cancel harmonics.  
   
   
       4 . The circuit of  claim 3 , wherein the second frequency is about half of the first frequency.  
   
   
       5 . The circuit of  claim 3 , wherein the first and second output signals belong to a baseband frequency.  
   
   
       6 . The circuit of  claim 4 , wherein one of the cancelled harmonics has a frequency of f 1 − 2 f 2 .  
   
   
       7 . A circuit for receiving a radio frequency signal comprising: 
 a first poly-phase filter for transforming a radio frequency signal having a first frequency (f 1 ) into two pairs of input signals, each having a different phase from other input signals;    a second poly-phase filter for transforming a local oscillator signal having a second frequency (f 2 ) into two pairs of drive signals orthogonal to each other;    a first mixer for mixing the two pairs of input signals with one pair of the two pairs of drive signals, to output a first output signal having a third frequency, the first mixer being operatively coupled to the first and second poly-phase filters; and    a second mixer for mixing the two pairs of input signals with a remaining pair of the two pairs of drive signals, to output a second output signal having a substantially same frequency as the third frequency, the second mixer being operatively coupled to the first and second poly-phase filters.    
   
   
       8 . The circuit of  claim 7 , wherein the first and second output signals are 90° out of phase with respect to each other.  
   
   
       9 . The circuit of  claim 8 , wherein each of the first and second mixers cancels harmonics.  
   
   
       10 . The circuit of  claim 8 , wherein the first and second frequencies are substantially the same.  
   
   
       11 . The circuit of  claim 8 , wherein the first and second output signals belong to a baseband frequency.  
   
   
       12 . The circuit of  claim 8 , wherein a cancelled harmonic has a frequency of f 1 −f 2 .  
   
   
       13 . A method comprising: 
 transforming a radio frequency signal having a first frequency into two pairs of input signals orthogonal to each other;    providing a first and second signal groups being 45° out of phase with respect to each other, signal group having two pairs of drive signals orthogonal to each other;    mixing the two pairs of input signals and the two pairs of drive signals of the first signal group to output a first output signal having a third frequency; and    mixing the two pairs of input signals and the two pairs of drive signals of the second signal group to output a second output signal having a substantially same frequency as the third frequency.    
   
   
       14 . The method of  claim 13 , wherein the first and second output signals are 90° out of phase with respect to each other.  
   
   
       15 . The method of  claim 13 , wherein the two pairs of input signals are mixed with the two pairs of drive signals of the first signal group in a first mixer, and 
 the two pairs of input signals are mixed with the two pairs of drive signals of the second signal group in a second mixer,    in a sub-harmonic double balanced active mixing mode adapted to cancel harmonics.    
   
   
       16 . A method comprising: 
 transforming a radio frequency signal having a first frequency into two pairs of input signals orthogonal to each other;    providing two pairs of drive signals orthogonal to each other and both having a second frequency;    mixing the two pairs of input signals and one pair of the two pairs of drive signals to output a first output signal having a third frequency; and    mixing the two pairs of input signals and a remaining pair of the two pairs of drive signals to output a second output signal having a substantially same frequency as the third frequency.    
   
   
       17 . The method of  claim 16 , wherein the two pairs of input signals are mixed with one of the two pairs of drive signals by a double balanced active mixing mode adapted to cancel harmonics.  
   
   
       18 . The method of  claim 17 , wherein the two pairs of input signals are mixed with the remaining of the two pairs of drive signals by the double balanced active mixing mode adapted to cancel harmonics.