frequency domain simulation.pdf
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1、Advantages of Frequency Domain Simulation for Wireless Transceiver Design Application Note Advantages of Frequency Domain Simulation for Wireless Transceiver Design 08/25/032 Introduction A radio transceiver, shown in the following diagram, provides modulation and demodulation functions to enable tr
2、ansmitting and receiving digital information through the air link. The radio is composed of a transmitter, a receiver in conjunction with automatic gain control (AGC) and automatic frequency control (AFC), and a synthesizer. These overall transceiver blocks are made up of many modules cascaded toget
3、her to process the information. The modules include modulators, demodulators, amplifiers (LNAs, Power Amps, IF Amps, etc.), mixers, oscillators, PLLs, AGCs, AFCs, and other RF components. Traditionally, RF Intermodulation distortion; and third-order intercept ? Power Added Efficiency (PAE) ? Adjacen
4、t Channel Power Ratio (ACPR) A load-pull simulation is easy to perform with RFDE. In such a simulation, a circular region on the Smith chart is specified, and load impedances within this region are presented to the output of the amplifier. Output power contour circles are plotted out and the optimum
5、 power point is then located. It is also easy to calculate DC-to-RF efficiency, and 3rd- and 5th-order intermodulation distortion versus load impedance at any bias point. The powerful and flexible data display capability enable designers to plot and apply the optimum conditions to meet their design
6、specs. Figure 5 shows an example of simulated load impedances, swept output spectrum and intermodulation distortion versus input power. Using this output with the specified contours, you can quickly determine how changing the load impedance affects the output power, efficiency, and level of intermod
7、ulation distortion products, as well as the shape of the output waveform. Figure 5. Load impedances, swept output spectrum, and intermodulation distortion versus input power. Parameter sweep is another valuable simulation technique in RFDE. Swept parameters results in plots that help designers do fa
8、st trade-offs to optimize results. Figure 6 shows an example of this. Trade-offs may be made between output power, DC-to-RF power efficiency, and DC bias current consumption. Figure 6 also illustrates the flexibility of the data display in presenting the data, making it easier for designers to make
9、trade-off decisions and optimize results. Advantages of Frequency Domain Simulation for Wireless Transceiver Design 08/25/037 Figure 6. Output Power and DC- to-RF Efficiency Versus Emitter Resistor and Versus Vin_Bias allow designers to make important design trade-offs. Optimization in the Frequency
10、 Domain Because results are always in spectral frequency domain, this makes it very easy for HB to process these spectral components and effectively optimize key results like distortion and spurious signals (-1 dB compression, IP3, ACPR, etc). RFDE frequency domain linear simulator is also capable o
11、f easily optimizing wide band filter structures, matching networks, and other parameters for gain, power, noise figure, VSWR, group delay, and etc. RFDE for Modulators An I-Q, or vector, modulator is a common integrated circuit in communication systems. These modulators take two baseband data sequen
12、ces (I and Q channels) and vary the amplitude and phase of a sinusoidal signal (the carrier) in response to the instantaneous I and Q channel voltages. Designers of these ICs must be concerned with a number of characteristics, some of which include: ? Modulation accuracy ? Frequency response ? Undes
13、ired leakage ? Intermodulation distortion terms ? Efficiency and output power ? Modulator amplitude and phase accuracy with realistic baseband data sources ? EVM Many of the I and Q modulator analysis and simulations would be almost impossible to complete with a purely time-domain simulator such as
14、SPICE. The RFDE “Circuit Envelope” simulator is very well suited and very efficient for such analysis. RFDE Circuit Envelope Circuit Envelope was developed specifically to efficiently simulate the transient and complex modulated RF signals found in todays wireless circuits. The main advantage of the
15、 mixed frequency/time domain approach at the base of Circuit Envelope is that it performs the simulation only in the relatively narrow frequency band that is occupied by the modulated signal. Unlike SPICE, it does not need to analyze the complete spectrum up to the maximum frequency Advantages of Fr
16、equency Domain Simulation for Wireless Transceiver Design 08/25/038 set by the simulation period. This results in an enormous time savings in getting the necessary results. Figure 7 illustrates this. Figure 7. Circuit Envelope is highly efficient in analyzing circuits with digitally modulated signal
17、s, because the transient simulation takes place only around the carrier and its harmonics. Calculations are not made where the spectrum is empty. Circuit Envelope simulation output is a time-varying spectrum from which useful information, such as PLL frequency Vs time transients, ACPR (adjacent chan
18、nel power ratio), EVM (error vector magnitude) and NPR (noise power ratio) can be derived. Such simulation can be carried on up to as many orders of harmonics the user specifies (5th, 7th, 9th.mixer intermodulation products analysis), and all analysis can be carried out down to the transistor level.
19、 Figure 9 shows a transistor level direct conversion IQ modulator, and the output results from the simulation that was run, with baseband signals corresponding to the IS-95 CDMA specification. The simulation took less than one hour to perform, and the resulting spectrum, output power, and ACPR are s
20、hown in the figure. Advantages of Frequency Domain Simulation for Wireless Transceiver Design 08/25/039 Figure 8. Transistor-level direct-conversion IQ modulator, along with spectrum, trajectory, main channel power, and ACPR results from an IS-95 CDMA baseband source applied to a transistor level di
21、rect conversion IQ modulator. Simulation time was less than one hour. Figure 9 shows the output trajectory, constellation diagrams, error vector magnitude (EVM) in Volts versus time, and percent EVM. Designers can introduce arbitrary values for these imbalances and observe the EVM degradation. Advan
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