wherein {HEAD ~ an output signal} showing a result of multiplication of said first and second input signals is differentially derived between said collectors or drains of said first and fourth transistors and said {TAIL ~ collectors} or drains of said second and third transistors 
wherein { HEAD ~ an output signal } showing a result of multiplication of said first and second input signals is differentially derived between said collectors or drains of said first and fourth transistors and said { TAIL ~ collectors } or drains of said second and third transistors
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH