Why the output waveform at summing amplifier is out of phase of 180 with input signal?

Answer 1

Because as the signal voltage increases on the base, the base current increases this causes the collector current to increase, this decreases the voltage drop Vc to ground. As the base voltage decreases the base current decreases causing the Collector current to decrease, increasing the voltage drop Vc to ground.

i think dis ans will clerify d doubts of students...

... in CE config..

as Vo=Vcc-Ic Rc nw as Vcc is const. v cn say Vo is directly proportional 2 (-Ic Rc) so nw when d base voltage is increased Ib will inc. thus, Ic will inc. cuz Ic=beta Ib thus Ic Rc drop increases... as Vo is prop 2 -Ic Rc thus, Vo will decrease...thus d curve for d +ve half cycle in which Ib is increasing drawn in 180 deg phase showing Vo is dec. n vice versa 4 -ve half cycle...

nw in CC...

as d o/p is taken frm emitter... Vo= Ie Re so der's no -ve sign..n for d +ve cycle Ie will incr(dat's leakage current) as der's no-ve sign it'll b in phase wid i/p..hence no phase shift as leakage current doesnt incr. so much thus,d o/p voltage Ie Re doesnt inc much thus, d o/p doesnt amplify much thus dis config knwn as emiter follower...

nw in CB,...

d I/P is appiled at emitter n o/p is taken frm collector... so, 4 d +ve half cycle d Eb junc will b more FB thus causing incr. in Ib n thus, in Ic... so inc. in Ic causes inc. in o/p voltage..n during -ve half cycle d junc will b less FB so o/p voltage will b decreasing..hence der's no phase shift...

for any other help..

cont.-

shrey.dhingra51@gmail.com

Answer 2

Because you're using an inverting amplifier. This will cause an apparent 180 degree phase shift.