Next step is to test performance of all stages at higher frequencies. All tests are performed in the same manner as in previous testing. Inputs of all 4 stages are connected together and transfer function of every stage is modified to have Gain=1 with corresponding loads and at 20 KHz. Read more
I will use my Total Harmonic Analyzer for LTSPICE to perform these tests. Control script is slightly modified, to decrease test (simulation) time. It is possible to do so, because all schematics are settling fast and we are not looking into very small THD numbers. Signal amplitudes are also of moderate values. Read more
Modulation of Input Capacitance.
Changing offset causes some changes in the frequency response. While AC analysis is small signal analysis, offset change will show some differences in big signal performance. One part of this change is modulation of Ccb capacitance. Read more
AC small signal gain, 8 Ohm load.
Overall gain for all 4 stages was evaluated on the following plots.
We will try to use similar colors for all comparison testing. Read more
Performance of output stage plays a significant role in overall performance of audio power amplifier and, together with VAS output stage, may be considered to be the major source of distortions. Read more
If you are estimating stability of feedback system, determining bandwidth or decoupling components for your circuit, RC time constant or cut-off frequency is one of essential parameters. This calculator will help you to evaluate cut-off frequency and time constant of RC circuit. Read more
FFT capabilities integrated into LTSPICE simulator are nice and flexible. However, if you would like to evaluate frequency or amplitude dependence of distortions, you have to take these measurements point by point and then manually plot them.
I created an LTSPICE add-on to automate THD measurements and plot result in the form of THD vs. Amplitude and THD vs. Frequency graphs. Read more
Here is an example of parametric sweep, showing one possible way of potentiometer and variable resistor simulation in LTSPICE. I will use commonly referenced tone control, originally suggested by James and modified by Baxandall to utilize active tone control scheme. Read more
TI recently updated their FilterPro™ MFB and Sallen-Key Filter Design software. It is not complete filter design suit and includes only limited amount of physical realizations of second order stages. In fact FilterPro™ is supporting only Multiple Feedback and Sallen-Key realizations of active stages. However, it is doing well what it supposed to do. Read more
Thermal noise of passive components makes big influence on overall noise performance. Values of passive components should be carefully evaluated, especially in case of low noise design. Otherwise, you will not be able to take advantage of low noise performance of active components.
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