上海交通大学：《通信基本电路》课程教学资源（参考资料）Mixers

Mixers RF IC for Wireless Communications Omar Wing Shanghai Jiao Tong University Omar Wing RF IC-Mixers 1 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 1 Mixers RF IC for Wireless Communications Omar Wing Shanghai Jiao Tong University

Mixer Function To convert an RF signal at fer to an IF signal at fir by "mixing"the RF with a signal at fo generated by a local oscillator (LO). LO Image Rejection LNA Mixer IF amp Omar Wing RF IC-Mixers 2 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 2 Mixer Function To convert an RF signal at to an IF signal at by "mixing" the RF with a signal at generated by a local oscillator (LO). RF IF LO f f f Image Rejection LNA Mixer IF amp LO RF f IF f LO f

Design Goals Mixing should generate only IF and no other frequency components. Conversion gain,IF/RF,should be high Conversion should be linear.Large IP3. Good dynamic range of RF. ·Low noise.Low power. Good isolation from strong LO. Omar Wing RF IC-Mixers 3 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 3 Design Goals • Mixing should generate only IF and no other frequency components. • Conversion gain, IF/RF, should be high. • Conversion should be linear. Large IP3. • Good dynamic range of RF. • Low noise. Low power. • Good isolation from strong LO

Ideal Mixer ARE COSOREt -y(t) ALo cos@Lot y(t)=ARF COS ORFt.ALo cOS@Lot 2isrineos(@u0ol加+7Asr4oeoow+oolr Yr()=Ame Aro COs(@wr-0o) Conversion gain =ALo/2 Omar Wing RF IC-Mixers 4 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 4 Ideal Mixer cos ARF RF  t cos ALO LO  t y(t) ( ) cos cos RF RF LO LO y t  A  t  A  t 1 1 cos( ) cos( ) 2 2 ARF ALO RF LO RF LO RF LO    t  A A   t 1 ( ) cos( ) 2 IF RF LO RF LO y t  A A   t C o n ve rsio n g a in = / 2 AL O

Square Law Mixer y(t)=(ARF coS@RFt+ALo cos@Lot) -ARF ALo COS(ORF-@LO)t+ARF ALo COS(@RF +@Lo)t dc terms+terms at 20gr and 20Lo YIF (t)=ARr ALo COS(@RF-@LO)t Conversion gain =ALo Omar Wing RF IC-Mixers 5 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 5 Square Law Mixer 2 ( ) ( cos cos ) RF RF LO LO y t  A  t  A  t cos( ) cos( ) ARF ALO RF LO RF LO RF LO    t  A A   t dc terms + terms at 2 and 2 .  RF LO ( ) cos( ) IF RF LO RF LO y t  A A   t Conversion gain =ALO

MOSFET Square Law Mixer Simple Mixer (Square Law) VLo 77T 0=4心s+g0-o旷 Vg(t)=ARE cOSωRFt vs (t)=ALo cos@Lot Omar Wing RF IC-Mixers 6 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 6 MOSFET Square Law Mixer 1 2 ( ) ( ( ) ( )) 2 d ox BIAS g s W I t C V v t v t L     ( ) cos ( ) cos g RF RF s LO LO v t  A  t v t  A  t

MOSFET Square Law Mixer dahncord Conversion gain LCoW (S) 2L RF/LO isolation is not good.LO appears as -2IBus ALo cos@Lot in i.A LPF need be inserted between the mixer and the IF amplifier. Omar Wing RF IC-Mixers 7 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 7 MOSFET Square Law Mixer ( ) 1 cos( ) 2 d IF ox RF LO RF LO W i C A A t L     Conversion gain = (S) 2 ox LO C W A L  RF/LO isolation is not good. LO appears as 2 cos in . A LPF need be inserted between the mixer and the IF amplifier. BIAS LO LO d  I A  t i

Multiplier-Type Mixers Use the MOSFET as a switch.Turn the RF signal on and off by the LO signal at a rate equal to fio.The output will contain frequency components at IF and around all the harmonics offio. Omar Wing RF IC-Mixers 8 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 8 Multiplier-Type Mixers Use the MOSFET as a switch. Turn the RF signal on and off by the LO signal at a rate equal to . The output will contain frequency components at IF and around all the harmonics of . LO LO f f

Single Balanced Mixer Single Balaneea Mixer 777m A differential signal Vo/-Vo is applied to M and M2 to steer the source current Ipc+Ig cos @t alternately to I or 1,.The differential output I-1,contains the desired IF and other frequency components. Omar Wing RF IC-Mixers 9 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 9 Single Balanced Mixer 1 2 1 2 1 2 A differential signal / is applied to and to steer the source current cos alternately to or . The differential output contains the desired IF and other frequency compon LO LO DC RF RF V V M M I I t I I I I     ents

Single-Balanced Mixer The current I(t)can be regarded as the source current lpicd ofperiod7ia=么。a and amplitudes 1 and 0. I(1)=Sq(t,TLo)(IpC+IRF cOS@REt) l,0-t--1nXle+lecosou0 Omar Wing RF IC-Mixers 10 Shanghai Jiao Tong University

Omar Wing RF IC - Mixers Shanghai Jiao Tong University 10 Single-Balanced Mixer Th 1 e current ( ) can be regarded as the source current 1 multiplied by a square wave of period and amplitudes 1 and 0. LO LO I t T f  1 2 ( ) ( , )( cos ) ( ) ( , )( cos ) 2 LO DC RF RF LO LO DC RF RF I t Sq t T I I t T I t Sq t T I I t       