Lect10_Mixers I

# Lect10_Mixers I - ECE 894 RF and mmWave Front-end Circuit...

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ECE 894 RF and mmWave Front-end Circuit Design Prof. Waleed Khalil Lecture Mixers I 10 1

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Mixer The mixer acts as a downconversion block in RX or upconversion block in TX In the simplest form, the mixing process can be viewed as a multiplication Due to mixer inherit nonlinearity, several unwanted frequency components are generated and need to be minimized LNA gain reduces the impact of mixer noise on RX Mixer NF is typically much higher than LNA NF (e.g. 10-15 dB) Mixer conversion gain reduces noise impact of subsequent RX blocks In CMOS, conversion gain is often quoted in voltage or current and not power Mixer linearity (i.e. IIP3 and IIP2) is most critical for RX blocker performance Need good isolation between mixer RF,LO and IF ports 2 NF, G p, IIP3 RF LO IF t) f cos(2 A RF RF π t) f cos(2 A LO LO Conversion Gain ( ) 2 LO V A A = )t) f (f cos(2 2 A A )t) f - (f cos(2 2 A A LO RF RF RF RF + +
Nonlinear Mixers 3 Frequency components: 1. DC term 2. Harmonics: nf RF , nf LO n =1,2,3,….N 3. IM products: mf RF +nf LO m,n =+/-1,2,3,…., m+n=N Need to filter out all components except f RF -f LO Filter challenge: How to filter out in-band IM products ?? t) f cos(2 A RF RF π t) f cos(2 A LO LO + i i0 () N = ) ( t y Order Nonlinearity th N

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Square-Law Mixer Removes majority of undesired IM frequencies Frequency components: 1. DC term 2. Harmonics: f RF , 2f RF , f LO and 2f LO 3. Intermod. products: f RF -f LO and f RF +f LO
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Lect10_Mixers I - ECE 894 RF and mmWave Front-end Circuit...

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