Question

d. A coherent detector is used to demodulate Amplitude Modulated Single Side Band Suppressed Carrier (AMssesc) as shown in Figure Q1(d). Explain mathematically the effect on the output signal Vo(t) when there is a phase difference between the AM ssesc and the local oscillator vo(t). (C01: P01 - 5 marks) Assasco X LPF voll v.0) Multiplier Figure Q1(d)

Answer 1

Soln)

General expression of SSB SC - AM SSB SC (t) = Amct) cosaatett Acmct) Sinzatat 2 2 SSB modulator AM SSB Sc(t) MC+) ((f) = Am Coszafct Hilbert ñ CE) mct Transform SSB SC - Demodulator K) Х L.P.F Volt) AMSssselt) Vect) = Ac Cos (2afct +0) = Phase difference b/w C(+) a Vect). x(+) = AMSSBSCC+)] Ac Cos(27fct +o) · XC+) = Amets cos2atct + Acmet) sin224e4 Accogle.atet +9) Xc15=EN 2 2 - Rejected by Liper = Ac mct) cos(untet to -0) + Ak mct) coso 2 + Ac nicio mct) sin (uffetto) – A A c m Ct) sind 4. Rejected by Lipif 2 Volt) = AC mct) coso A 2 ñct) sind when, o=0 ńct) Volt) = Ac mct) 4 when d=90 2 A Volt) = Acne 4 Since Vo(t) to Wence SSB SC is not affected by the Quadrature null effect cuf Demodulator.