RF & Wireless Figure 6:
RF & Wireless Figure 6: Example of the equivalent schematic of the bond wires The electromagnetic compatibility (EMC) and signal integrity were analyzed in the time domain, where a series of bits were transmitted through the system. The binarity of the system provides robustness, but issues in the schematic design with the impedance of the IP pins, phase shifts, reflections, and cross-talks caused distortion of signal quality and failure to receive the correct bits. The bit error ratio (BER) indicated that there were significant problems in the design. Figure 1 shows the 3D layout in Analyst of the Infineon BJT package. On a circuit level, the eye window for the signal is usually defined, the estimate of which allows distortion of the signal in all possible bit sequences. All these effects require high-quality models for simulation of modern cutting-edge systems to control them. Nonlinear components are included in addition to linear parasitic nonlinear effects. There are such formats as SPICE, IBIS, Touchstone port parameters, and more, which model the linear and nonlinear components and enable the design of analog, digital, or mixed-signal systems. The SPICE model is a very popular simulation model that uses text files to present the equivalent schematic of the device with parasitic effects. It usually presents the physical structure of the device, which gives very good simulation quality, but opens the internal structure of device. The quality of modeling, as well as the design quality and speed, influence the economic aspects of the design. High-quality models reduce design time, as well as design and prototyping costs, because they require less redesign and prototype iterations, enabling earlier time to market and higher market share for electronic products. This is particularly important for nextgeneration technologies such as internet of things (IoT) and 5G communication systems, as systems with such complexity, density, and frequency range cannot be properly designed without precise modeling. Measurement Equipment and Settings SPICE model development starts with an adequate EM model. The EM model should correspond to the real device, therefore the geometry and electric properties of the materials, as well as port settings of model, should correspond to the real-world material and user case. Comparison of the EM model simulation with measurements lets designers verify how close the EM model is to the real device. The calibration of measurement setup and consideration of the parasitic effects is another task required for correct comparison. When the EM simulation is close to the measurements, it can be used for EM extraction. A good way to compare the EM model with the real device is to compare the S-parameters obtained during EM simulation and measurements. Figure 7: 1.5 W amplifier gain, output power, and efficiency after optimization for 12 V operation SPICE Extraction SPICE format is one of the most commonly-used simulation models for EDA software tools. It can model linear and nonlinear circuits and include parasitic effects of the components. Including the main parasitic effects in the SPICE netlist makes possible correct wideband behavior of the model. S-parameters are 46 hf-praxis 8/2018
RF & Wireless Figure 8: Schematic of the entire model also often used for simulation of high-frequency devices, but this approach provides linear behavior only on the device pins, does not include the inner structure of the device (black-box model), and is not supported in many simulators, unlike SPICE. Usually S-parameters are the result of a measurements with certain temperature, calibration, and more. They have many advantages, but SPICE is more flexible and includes more information. SPICE can present an equivalent schematic in an EDA tool or in text format. The review of existing SPICE models for packages shows that many electrical effects are not included in models. This reduces their precision and doesn’t provide good correlation with measurement versus frequency. This can be seen after a comparison of measurement and simulation of these models. As a result, simulation results can’t predict measurements of modeled devices. Such differences can have a negative impact on the development of RF devices. For instance, a bad SPICE model will provide a wrong impedance calculation and the matching circuit will be calculated for the wrong impedance. This will cause the measured device to perform poorly. Only high-quality models can do this correctly and deliver an accurate prediction of circuit performance. Figure 4 shows an example of such a model. Often models are done only for small frequency bands. For this, using S-parameters is sufficient, as they will be closer to the measurement. In the next section a SPICE model extraction procedure is described. NI AWR Design Environment, specifically Microwave Office circuit simulation software, was used for extraction Figure 9: Testing for Pin 1 hf-praxis 8/2018 47
