A radio-frequency transceiver comprising a receiver and a transmitter is the main system responsible for establishing communication between users of the communication system. This lecture focuses on the study and design of radio-frequency receivers. The course starts with an overview of important design specifications for both a transmitter and a receiver. Common specs such as frequency bands and channelization, data rate, type of modulation, transmitter output power and spectral mask, the transmitter EVM, receiver sensitivity, receiver input level, and receiver tolerance to blockers will be briefly discussed. The course then will provide an in-depth study of wireless receivers. Starting with bandpass representation of RF signals, the need for the quadrature downconversion to fully recover the signal is discussed. The course will then go over the concept of heterodyne architecture and investigates the problem of image in this architecture. The students will learn that a heterodyne receiver always faces a trade-off between channel selection and image rejection. Next, the widely used direct-conversion receiver architectures will be studied. The course provides a deep study of all issues in regard to the direct-conversion receiver including the local-oscillator leakage, the DC offset, even-order distortion, I/Q imbalance, and the impact of 1/f noise. Next, the image-reject architectures will be studied and a powerful graphical analysis is utilized to analyze these architectures. The course will go over the low-IF receivers and polyphase filters. Finally, the dual-quadrature downconversion receivers based on the concept of complex mixers will be studied.
An overview of the course is provided. Materials covered in this course include:
- An overview of the wireless systems' performance parameters
- Heterodyne receiver architectures and issues associated with this structure
- Direct-conversion receiver architectures and issues associated with this structure
- Image-reject receivers including Hartley and Weaver schemes
- Low-IF receivers
- Polyphase filters
- General considerations
- Wireless standards and link budget. Common specs including:
+ Frequency bands and channelization
+ Data rate
+ Antenna duplexing method
+ Types of modulation
+ TX output Power and spectral mask
+ TX EVM
+ RX sensitivity
+ RX tolerance to blockers
- Solving a useful example on the communication link budget
- Basics of RF receivers
- Introducing low-side injection
- Introducing high-side injection
- An overview of bandpass representation of RF signals
- The need for quadrature mixing in zero-IF downconversion
- Introduction to heterodyne receivers
- A comparative study of direct conversion and heterodyne receivers
- The problem of the image in heterodyne receivers
- Trade-off between image rejection and channel selection in heterodyne receivers
- Dual downconversion receivers
- Mixing spurs
- Dual downconversion receivers with zero second IF
- Why downconversion to zero-IF frequency is done by a quadrature downconversion stage
- Direct conversion receiver (DCR) architecture
- DCR vs. heterodyne
Solving two examples:
1. Mixing spurs in a DCR
2. A dual downconversion RX with zero second-IF. the second LO is half the first LO frequency
- DCR vs. heterodyne receiver
- Issues in a DCR
+ LO leakage
+ DC offsets
+ Even-order distortion
+ I/Q mismatch
+ Flicker noise (1/f noise)
+ Mixing spurs
- LO leakage
- DC offsets
- Examples and methods to overcome LO leakage and DC offset
- Original root cause of even-order distortion
- Even order distortion causing the problem of beat frequency due to strong in-band interferes in a DCR
- Even order distortion causing the problem of unwanted AM demodulation of QAM in a DCR
- Studying the root cause of I/Q mismatch
- Why is it more important in a DCR compared to a heterodyne RX?
- Analysis of phase and amplitude imbalances
- Explanation of the need for image-reject architectures with no explicit image-reject filtering
- Signal analysis of a 90-degree phase-shifting mechanism
- An insightful graphical approach in studying the 90-degree phase shift
- An intuitive analysis of image-reject architectures using a three-dimensional spectral plot
- Studying the spectral impact of 90-degree phase shift and Hilbert transform
- Quadrature downconversion stage as a way of realizing a 90-degree phase-shift
- Studying the low-side and high-side injections in a quadrature downconversion stage
- Introducing step-by-step analysis and synthesis of an image-reject architecture
- A study of Hartley architecture
- A review of the issues in Hartley architecture
- Defining image-rejection ratio (IRR)
- An overview of issues in Hartey architecture
- Introducing Weaver architecture based on intuitive spectral analysis
- Issues in Weaver architecture including
1. the need for two more mixers and an additional LO compared to Hartley
2. the problem of the secondary image
- A comprehensive study of the fundamentals of polyphase filters
- Analyzing the polyphase filters in image-rejection receiver architectures
- Study and design of polyphase filters to improve the image-rejection ratio
- Introducing the concept of complex mixers and the corresponding system design
- The use of the complex mixer in a double-quadrature receiver architecture
- Why is the problem image non-existent in a double-quad receiver?
- Ccomprehensive analysis of gain and phase errors in a double-quad receiver
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