Introduction to RFIC receiver architec-

ture

Special Topics in Computers and Circuits30(Wed), March, 2011

2007144078 Min, Kyungsik

Context• Terminology

– Local Oscillator (LO)– Low Noise Amplifier (LNA)– Intermediate Frequency (IF)

• Receiver Architecture– Heterodyne– SuperHeterodyne– Direct-Conversion (Zero-IF)– Low-IF– Quasi-IF

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Terminology

Receiver Architecture

Local Oscillator(LO)• converting a signal of interest to a different frequency using a mixer (by wikipedia)

• Heterodyning : process of conversion• produces the sum and difference frequencies of the frequency of the local

oscillator and frequency of the input signal of interest.

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LNA• first amplifier in the receiver, right after the antenna and the duplex filter

• To boost the received signal out from the noise and reduce the noise interference

• The gain of the LNA helps to suppress the noise of the subsequent blocks in the receiver.

Frii’s Equation++…

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Intermediate Frequency(IF)Definition • a frequency to which a carrier frequency is shifted as an intermediate step

in transmission or reception• Created by mixing the carrier signal with a local oscillator signal

• Used in superheterodying radio receivers

Merits• can be used in many devices

• To convert the various different frequencies of the stations

• Improve frequency selectivity

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Intermediate Frequency(IF)• Television receivers: 30 MHz to 900 MHz

• Analogue television receivers using system M: 41.25 MHz (audio) and 45.75 MHz (video). Note, the channel is flipped over in the conversion process in an intercarrier sys-tem, so the audio IF frequency is lower than the video IF frequency.

• Analogue television receivers using system B and similar systems: 33.4 MHz. for aural and 38.9 MHz. for visual signal.

• FM radio receivers: 262 kHz, 455 kHz, 1.6 MHz, 5.5 MHz, 10.7 MHz, 10.8 MHz, 11.2 MHz, 11.7 MHz, 11.8 MHz, 21.4 MHz, 75 MHz and 98 MHz.

• AM radio receivers: 450 kHz, 455 kHz, 460 kHz, 465 kHz, 470 kHz, 475 kHz, 480 kHz

• Satellite uplink-downlink equipment: 70 MHz, 950-1450 Downlink first IF

• Terrestrial microwave equipment: 250 MHz, 70 MHz or 75 MHz

• Radar: 30 MHz

• RF Test Equipment: 310.7 MHz, 160 MHz, 21.4 MHz

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Terminology

Receiver Architecture

Heterodyne receiver

• Traditional heterodyne receiver architecture based on the parallel data detector concept

• the original radio receiver design• introduced in 1901 by Reginald Fessenden (Canadian inventor-en-

gineer)

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Heterodyne receiver• exploits high quality filters to provide desired performance

1st filter : duplex filter

2nd filter: image rejection fil-

ter 3rd filter

: channel selection fil-ter

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Heterodyne receiverProblem #1 : It is very difficult to tune an amplifier and/or filter!

• We can change the frequency response of an amplifier/filter by changing the values of the reactive components(i.e., inductors and capacitors).

• But the center frequency and bandwidth of an amplifier/filter are related to the inductor and capacitor values in very indirect and complex ways.

• Additionally, a filter of high selectivity(i.e., “fast roll-off”) will be a filter of high order -> high order means many inductors and capacitors!

Result : Tuning a good heterodyne receiver can be very difficult, requiring a precise adjustment of many control knobs!

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Heterodyne receiverProblem #2 : The signal reaching the detector can be any one of many frequencies(e.g., w1, w2, w3, w4) distributed across a very wide band-width.

As a result, the detector must be wideband!

Unfortunately, a good wideband detector/ demodulator is difficult to build. Gen-erally speaking, a detector/demodulator will work well at some frequencies, but less well at others.

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Superheterodyne receiver• superheterodyne : creating a beat frequency that is lower than the original

signal

• to purposely mix in another frequency in the receiver, so as to reduce the signal frequency prior to processing

Incoming signal, centered at the carrier frequency

Intermediate frequency signal, at constant frequency, IF

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Superheterodyne receiver• Advantages of using Superheterodying (receiver)

– Reduces the signal from very high frequency sources where ordinary components wouldn’t work(like in a radar receiver)

– Devices can be optimized or made more inexpensively

– Can be used to improve signal isolation by arithmetic selectivity

• Difficulty– Hard to treat high quality of digital signal

– Duplication of original signal and image signal

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Direct-conversion

Direct-conversion receiver architecture

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Direct conversion

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Direct conversion• Amplification and filtering : performed at baseband

– Low current drain in amplifiers and active filters– No task of image-rejection

• Wide tuning and high selectivity

• Two high frequency conversion stages in parallel• LO frequency deviation• Spurious LO leakage• DC offset connected to direct-conversion

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Low-IF

Low-IF receiver architecture

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Low-IF

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Low-IF• Analog implementation : hard to provided superior performance and a de-

gree of flexibility → downconversion of information signal to a low-IF frequency

• no duplication of desired signal with image frequency

• power consumption

• Use of I/Q-demodulation

• I/Q demodulation providing for 20-40 dB’s of image rejection → a less selective filter

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Quasi-IF

Quasi-IF receiver architecture

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Quasi-IF• Combining a non-tunable I/Q down-conversion mixer and a tunable image

rejection mixer for down-conversion to baseband and channel selection

Advantages• first LO : optimized with respect to phase noise as no switching require-

ments are now present

• Tunable second LO : operates at low frequencies whereby phase noise and undesired non-linearities may be minimized

• absence of IF filter

Disadvantages• DC offset

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ComparisonHeterodyne Direct-con-

version Low-IF

Selectivity Low High HighAnalog Re-quirements High Moderate Low

Flexibility Low Low HighCMOS Compati-bility Low Moderate High

Noise Low Moderate LowDynamic Range High High High

Comparison of various receiver architecture key parameters

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ComparisonAdvantages Difficulties

Direct-conver-sion

• No IF filters(2 LPFs)• No image• Low power consumption• Easy integration

• LO leakage• DC offset due to device

mismatch• 1/f noise• High linearity mixer

Low-IF • Low freq. low Q BPF• No LO leakage• No DC offset• Easy integration

• Image rejection• Path matching• Increased hardware than

direct-conv.Quasi-IF • No IF filters(2 LPFs)

• No LO leak• Low phase noise• Easy integration

• Image rejection• Path matching• Increased hardware than

direct-conv.

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Thank you.