Normally, {TAIL ~ the demultiplexer} and the multiplexer are controlled by the tone switching logic ciruit so as to alternately couple, at the multiplex frequency, {HEAD ~ the mixed signal} to the inputs of the first and second filters, and the outputs thereof to the squarer 
Normally , { TAIL ~ the demultiplexer } and the multiplexer are controlled by the tone switching logic ciruit so as to alternately couple , at the multiplex frequency , { HEAD ~ the mixed signal } to the inputs of the first and second filters , and the outputs thereof to the squarer
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH 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