Telecommunication Circuit Design

A CMOS wide output voltage swing DM modulator for envelope tracking technique

“…And the capacitor C will charge up approximately to the peak value of Vj n . When V in is less than V out across the capacitor, the diode conduction will be cut off and the capacitor will start to discharge through the resistor R with the voltage falling off exponentially [33]. Here it is assumed that an amplitude modulation (AM) signal has the form [34] V, = A 0 (l + mcosG) t)sind)J where A 0 is the amplitude, co s is the modulating signal angle frequency, co c is the carrier angle frequency and m is the modulation index.…”

“…+m cos co J) I + 5COS(CD C O-2 2; cos(2kco t) ~1 4F-1 J -J(l +wcosco 5 0 + -fcosco c^ + ^(cos(o) c + co^)r+cos(co c -co s )Oj cos (2k(o c t) m ( cos (2k& c + (a s )t + cos (2k(a c -(o s )tj^33) one can see that the output signal includes many frequency components: the modulating co s , the carrier oo c , the sidebands with frequency oo c + (o s , co c -a> s , the even harmonics of carrier 2&oo c and the sidebands with frequency 2&co c + co s , 2k(o c -(o s . In general, the modulating frequency G> S is much lower than the carrier oo c , so a simple RC network can be used to filter out the higher frequency components.In a CMOS technology, an ideal diode can not be realized.…”