# divide-by-N LO injection & phase accuracy

Question asked by jejo86 on Jan 18, 2013
Latest reply on Jan 22, 2013 by enash

hello,

i have two general questions concerning the quadrature demodulators.

why do all of the quadrature demodulators you offer have a divide-by-2 or in general divide-by-N local oscillator (LO) injection? what is the purpose/advantage of this circuit? why can't i input my LO-signal directly and it just gets shifted by a 90°-phase-shifter?

what does the phase accuracy mean exactly? if i wanted to simulate the demodulator, how would i do that. lets say my LO-signal is the following:

s_LO= sin(2*pi*f*t)

after the divide-by-2 and the phaseshift i get two mixing signals. lets say the phase accuracy is delta_phi=0.5°. would my mixing signals be:

s_inphase = sin(2*pi* (f/2) *t +- delta_phi) = sin(2*pi* (f/2) *t +- 0.5°)

s_quadphase = cos(2*pi* (f/2) *t +- delta_phi) = cos(2*pi* (f/2) *t +- 0.5°)

or

s_inphase = sin(2*pi* (f/2) *t +- (delta_phi/2) ) = sin(2*pi* (f/2) *t +- 0.25°)

s_quadphase = cos(2*pi* (f/2) *t +- (delta_phi/2) ) = cos(2*pi* (f/2) *t +- 0.25°)

?

and how is the the delta_phi distributed? can i assume it is equally distributed between -0,5°<delta_phi<+0,5° ? are there any statistics?

thank you

jejo86