Lecture #10 - Transceiver Architectures Part 1 Flashcards
What’s the difference between duplex and simplex?
Duplex; can transmit as well as receive RF signal
Simplex; one way communication is used
Name the different types of transceiver architectures
- Superheterodyne; Most sensitive, oldest and still one of the most popular
- Direct conversion/Homodyne; The one that is used in your mobile phone.
- Low-IF; To mitigate some of the issues of Zero-IF (trade-off)
- Digital-IF, Bandpass Sampling; ADCs/ADCs have an ultra-high speed and an acceptable power consumption
How do we select the transceiver architecture?
- Performance requirements: Tx power, Rx sensitivity,
- Economical aspect: cost, size, weight
Explain the Heterodyne process
- Core of heterodyne process lies frequency translation or mixing
- Tx; up-conversion IF->RF
- Rx; down-conversion IF->RF
The frequency translation can be performed in several steps
Describe the Full-Duplex Superheterodyne (Rx - RF Block) in terms of: Duplexer, Low Noise Amplifier, RF BPF
- Duplexer; Two bandpass filters.
- Use WFDM, so we use certain band for the receiver and transmitter respectively. Duplexer has BPF which chooses these bands of frequencies.
- Make sure Tx doesn’t enter Rx (Tx leakage), having a nice stop-band attenuation as high as possible.
- Low noise amplifier: amplifier with a low NF
A low NF in the beginning ensures a low cascaded NF for the Rx -> high sensitivity
Stepped-controlled gain -> high dynamic range
- RF BPF: A SAW filter with high selectivity
Suppresses Tx leakage, image and other interferences.
3.
For the Full-Duplex Superheterodyne Rx; What can you say about the BW of the Rx band select filter and RF BPF? Are they the same or different? Why?
Is an RF BPF necessary when talking about the full-duplex superheterodyne rx
Describe the Full-Duplex Superheterodyne (Rx - RF Block) in terms of: RF Amplifier, Local Oscillator, Buffer amplifier, Down-conversion mixer
- RF Amplifier; preamplifier of the mixer
- A high gain RF amplifier reduces influence of the mixer’s NF on the cascaded NF of the Rx -> higher sensitivity
- Local Oscillator
- Provides LO input to the down-conversion mixer
- LO sharing between Rx and Tx lowers power consumption and transceiver cost.
- Buffer amplifier; ensures sufficient LO power level to drive the mixer
- Down-conversion mixer; converts the Rx signal frequency from RF to IF
What are the different part of the full-duplex Superheterodyne
RF Block
- Duplexer
- Low noise Amplifier
- RF Bandpass Filter
- RF Amplifier
- Local Oscillator
- Buffer Amplifier
- Down-conversion mixer
IF Block
- IF BPF
- IF Variable Gain Amplifer
IF & BB Block
- IQ Modulator
- BB LPFs
- BB Amplifier
Describe the IF Block in a Superheterodyne Transceiver
- IF BPF; High sensitivity SAW filter used to select the desired channel
- Building a high-Q filter at fixed IF is easier than building a high-Q filter with tunable IF.
- IF is fixed and LO is tuned to select different channels in a band.
- IF VGAs; most of the gain in an Rx chain is achieved in the IF block:
- Power consumption for realising high gain at IF is significantly lower than at RF
- IF amplifiers do not require a high dynamic range, since strong interferes are suppressed by the filters.
Describe the Full-Duplex Superheterodyne Rx - IF & BB Block
- In-Phase and Quadrature (IQ) Demodulator; the IF signal downconverted into two BB components; I and Q.
Equal magnitude and 90 degree phase difference.
- BB LPFs; Acts as anti-aliasing filters. Sampled by an ADC at a rate of f_s > 2B Hz.
- BB Amplifiers; I&Q signals are amplified and converted to digital domain by ADCs sampling at f_s> 2BHz
What are the different components in Full-Duplex Super-Heterodyne Tx
BB and IF Block
- DACs and BB LPFs
- IQ Modulator
RF Block
- Up-conversion mixer
- Local Oscillator
- Buffer amplifier
- RF Amplifier and RF VGA
- RF BPF
- Power Amplifier
- Isolator
- Duplexer
Describe the BB and IF Block
- DACs and BB LPFs
BB signal is converted into analog domain and subsequently filtered in both I- and Q-channels.
- IQ Modulator
BB signals are upconverted to I- and Q-channel IF signals.
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We might even have an IF VGA; composite IF signal is amplified to an optimum level before it is upconverted to RF using the up conversion mix
However, no need for an amplifier. Might even distort a signal.
On what
RF Block
- RF Amplifier and RF VGA
- RF BPF
- Power Amplifier
- RF Amplifier and RF VGA
RF signal power level amplified to drive the power amplifier (PA)
- RF BPF
A high selectivity SAW filter suppresses the undesired mixing products generated by the up-conversion mixer.
- Power Amplifier; high gain and highly efficient RF amplifier.
- Ensures an optimum power level of the transmitted RF signal after deducting the insertion loss of the isolator and duplexer.
