תכנון מקלט RF ב-NI AWR Design Environment

פורסם ב-ינואר 27, 2016

מהנדס הפיתוח של חברת Cover Sistemi האיטלקית מציג לקוראי Techtime את המתודולוגיה והשיטה שבה תוכננה מערכת RF-UWB באמצעות תוכנת AWR של נשיונל אינסטרומנטס

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מהנדס הפיתוח של Cover Sistemi האיטלקית מציג לקוראי Techtime את השיטה שבה תוכננה מערכת RF-UWB בתוכנת AWR של נשיונל אינסטרומנטס

הפרוייקט המוגמר
הפרוייקט המוגמר

חברת Cover Sistemi האיטלקית הפועלת מעיירה קטנה ליד מילאנו, התמודדה עם אתגר לפיתוח מקלט RF בעל רוחב פס גדול מאוד (ultra-wideband – UWB). המתכננים נדרשו לספק תכנון מלא מרמת המעגל המודפס ועד האנטנות והממשקים האלקטרוניים, בהרצה אחת בלבד. החברה השתמשה בתוכנת התיכנון NI AWR Design Environment Microwave Office של חברת נשיונל אינסטרומנטס (NI).

היא השלימה את המהלך כולו, משלבי התכנון הראשונים ועד בניית אבטיפוס עובד, בתוך שבעה חודשים. במאמר המובא למטה מתאר מנהל פרוייקט הפיתוח, אליסיו קצ'יאטורי, את השלבים המרכזיים והשיקולים העיקריים שנעשו במסגרת הפרוייקט.

The design began with the high-level design and system performance optimization, then progressed to a complete schematic, RF layout, and, finally, electromagnetic (EM) design optimization. The layout was implemented on a PCB with six metal layers. The UWB receiver had a target sensitivity of -92 dBm with pulses occupying >1GHz bandwidth.

Antenna

The UWB receiver includes an antenna previously designed by Cover Sistemi for UWB radar devices. The antenna uses a non-standard elliptical radiator with floating reflector for gain enhancement. Figure 2 shows the antenna and its radiation pattern. Figure 3 is the input reflected power (S11) performance over the intended frequency range.

Figure 2. UWB antenna and its radiation patterns.
Figure 2. UWB antenna and its radiation patterns
Figure 3. S11 plot for the antenna over the UWB frequency range.
Figure 3. S11 plot for the antenna over the UWB frequency range

Receiver Architecture

An I/Q direct conversion architecture was selected, with analytical signal extraction at the baseband. This includes the antenna and an input bandpass filter, a low noise amplifier (LNA), a pair of mixers fed with quadrature LO signals, baseband lowpass filters, amplifiers and squaring detectors, and, finally, at the output for delivery to the next stage, analog-to-digital (A/D) conversion and digital processing.

Low Noise Amplifier

The LNA design, including the bias-tee that provides DC power to the active devices, was executed using AXIEM 3D planar EM simulator. The core amplifier and RF filter were co-designed to simultaneously obtain the desired out-of-band rejection, gain, and noise figure performance. Figure 4 shows nonlinear performance using real data as input.

Figure 4. LNA nonlinear performances evaluation with real data as input.
Figure 4. LNA nonlinear performances evaluation with real data as input

Mixer

The I/Q downconverting stage uses a broadband commercial mixer. Performance was tailored by means of distributed input filtering. EM simulation (AXIEM) of the I/Q downconverter is shown in Figure 5.

Figure 5. Gain vs. frequency results of the full layout EM simulation compared to the circuit simulation
Figure 5. Gain vs. frequency results of the full layout EM simulation compared to the circuit simulation

Full-Chain Simulation/Validation

The entire signal chain was simulated at the post-layout level, with each block using its AXIEM model (hierarchical extraction). Simulation used two different domains (RF/ZIF) with a very large number of harmonics, as required for a UWB signal. Multi-rate harmonic balance (MRHB) was also used to perform the simulation of the entire receiver up to the A/D converter. Real data from transmitted signal measurements were imported for the MRHB simulations. Figure 6 presents the results nonlinear signal-to-noise ratio (SNR) evaluation versus input power.

Figure 6. Nonlinear SNR evaluation vs. input power
Figure 6. Nonlinear SNR evaluation vs. input power

Formal Check, Sign-off and Production Phase

The entire board (six metal layers) was designed in Microwave Office, thus the entire design and simulation flow used NI AWR Design Environment tools. This sequence of pre-production steps was followed, to avoid missing steps: 1. Design rule check (DRC) :  need to verify that no PCB supplier rules are violated.

2. Layout vs. schematic (LVS): are we OK with layout? 3. Production / fabrication data: Gerber, Validation data for customer’s approval of production steps, BOM, Pick & place

Redesign of the schematic and layout with another EDA tool for PCB manufacturing was considered, but such an additional task would have been time consuming and would have required licensing costs if the tool was not already available in house. There is also the risk of errors in exporting/importing the layout between tools.

Design Rule Check — DRC was easy with the declaration of layout rules based upon the PCB supplier specifications for the following: 1. Metal min size/spacing. 2. Via aspect ratio/covering. 3. Minimum solder mask opening in presence of leads. 4. Solder paste.

Layout vs. Schematic — LVS analysis assured that there was connectivity on each layer, layer connections by vias, and device connections to top/bottom layer by means of solder mask openings. 

Production Files: Gerber/Drill — Gerber and drill echelon files were extracted and sent for board production.

Bill of Materials / Pick & Place —On a small board with few components, this would be easy to do by hand, but in this case there were more than 500 components. Exporting the layout to a different tool for this task has the risk of errors due to file incompatibility. Performing the generation of BOM / pick-and-place data with custom programming was the result.

The pick-and-place output file therefore included the data int the following list: RefDes (unique string ID of the device), Component ID (from AWR Vendor Libraries) for material acquisition, Library, X coord from board origin, Y coord from board origin, Rotation (degrees) and Mounting layer. 

Summary

A complete UWB RF receiver from antenna to A/D input was designed using NI AWR Design Environment for all phases of the design, including circuit design and layout, EM simulation (AXIEM), harmonic balance simulation, and PCB design. Bill of materials and pick-and-place specifications are not included in the tool set, so custom programming for these operations was done via the Microwave Office scripting tool.

Although a significant task, this was done in a straightforward manner, allowing these manufacturing setup capabilities to be included in the same single design platform. The advantage of using one design platform for the entire development process combined with rigorous design efforts and attention to layout details resulted in a prototype with first pass success.

פורסם בקטגוריות: Wireless , כללי