ee4101 lectures 6 -- 2010

ee4101 lectures 6 -- 2010 - EE4101 RF Communications Part B...

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1 EE4101 RF Communications Part B Prof TS Yeo
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2 EE4101 RF Communications Part B – Receivers Simple frequency conversions Rectification Envelop detection Mixing
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3 EE4101 RF Communications Part B – Receiver Simple transmitter Input: baseband signal at f m (voice, Video, or data), lowpass filter Mixing: up-conversion, local oscillator f c >> f m , product is f c f m and f c + f m Power amplification and radiation
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4 EE4101 RF Communications Part B – Receiver – superhetrodyne receiver Antenna received signal, amplified by LNA (low noise amplifier – to increase signal strength and reduce noise dependency of later stages) Down conversion: local oscillator f 0 = f c –f IF (or f 0 = f c + f IF ) mixed with received signal to produce f IF –f m (or f IF + f m - often filtered out) Bandpass filter, amplification (high gain, narrow bandwidth), detection Note: If the received signal is strong enough, detector could be used at the first stage
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5 EE4101 RF Communications Part B – Receiver Receiver noise: from amplifiers and diode detector Detector noise proportional to 1/f, however, at very high frequency, white noise (frequency independent noise) becomes predominant. Advantages of Superhetrodyne Minimize detector noise (can tune f IF ) Can tune IF easily No need for wideband RF amplifier
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6 EE4101 RF Communications Part B – Principle of Frequency Conversion Nonlinearity: use – frequency conversion; problem – noise generation ) 1 ( e I i v d S d i v v I G v G I v d i d v d i d I v i o d d o o d d d d V v d d V v o d o d ... 2
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ee4101 lectures 6 -- 2010 - EE4101 RF Communications Part B...

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