![]() This helps us to improve the way the website works, for example, by ensuring that users are easily finding what they are looking for. Analytics/Performance Cookies: These cookies allow us to carry out web analytics or other forms of audience measuring such as recognizing and counting the number of visitors and seeing how visitors move around our website. They either serve the sole purpose of carrying out network transmissions or are strictly necessary to provide an online service explicitly requested by you. The cookies we use can be categorized as follows: Strictly Necessary Cookies: These are cookies that are required for the operation of or specific functionality offered. A modified method, which is not discussed here, must be used if the plot should be displayed with the angular frequency ω. The standard Bode plot displayed in LTspice is given as a function of frequency f. The frequency response of a circuit can be simulated relatively easily with LTspice. If you double-click, you will get two cursors that will give the absolute value at each cursor position and the difference between the two cursor positions in a separate window. It is necessary to click on the waveform node title at the top of the graph. To read the exact values from the plot, it is possible to add cursors that you can move along the graph. Frequency response as a function of frequency f for a second-order low-pass filter. The amplitude gain is given in decibels on the y-axis on the left, and the phase shift is given in degrees on the y-axis on the right.įigure 2. Now the frequency response of the circuit will correctly show with the amplitude response and the phase response.įigure 2 shows the frequency response of a second-order low-pass filter as a function of frequency. For this, the function must be given as the ratio V(output)/V(input) in the Expression Editor. The frequency response of a system is yielded from the ratio of the output signal to the input signal the display still must be adapted slightly. After the desired node in the circuit (output) has been selected, the amplitude and the phase are displayed as a function of frequency. After the simulation successfully completes, an empty probe editor automatically opens. Now the actual simulation can be run ( Simulate > Run). In the voltage source parameters under menu item Small Signal AC Analysis, the desired amplitude is specified (1 V here). In addition, for the AC analysis, the input voltage with which the circuit should be stimulated should be defined. The remaining parameter information should be added as required. Under Type of Sweep, the value Decade should be selected. The x-axis in a Bode plot should have a logarithmic scale. The simulation parameters are also entered here. This requires an AC sweep, which can be found under the AC Analysis tab in the menu Simulate > Edit Simulation Cmd. The circuit will be stimulated with a sine wave. Example of a circuit for a second-order low-pass filter. The input and output nodes were given labels to facilitate the later display of the simulation in the simulation window.įigure 1. Figure 1 shows a second-order low-pass filter. To obtain the frequency response of a circuit, or its Bode plot, using LTspice, it helps to start with a simple circuit example. Thanks to its compatibility with SPICE, LTspice can handle numerous electronic components. In addition, small signal analyses and Monte Carlo simulations can be performed. With this powerful simulation software for analog circuits, signals in the time domain can also be transformed to the frequency domain. The frequency response of an electrical circuit can be simulated with LTspice ®. Simulation of the Frequency Response with LTspice Further advantages of the logarithmic representation are the larger frequency range of the plot and the identical relative precision over the entire curve. The phase responses can be additively superposed even without the logarithmic scale. If there are several partial transfer functions, the actual multiplication of their amplitude responses is simplified to an addition through the decibel scale. The amplitude response is given in decibels, so it is possible to construct complex Bode plots by superposition of simple subplots. For this, the amplitude response and the phase response are determined from the transfer function of the system and plotted as a graph with the gain and the phase as a function of frequency. This is called the frequency response of the system. For the development of dynamic systems in electrical engineering, control engineering, and even mechatronics, the steady-state response at the output of the system to harmonic excitation (sinusoidal oscillation) at the input often must be known. ![]()
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