 drives the circuit into non-linearity then it will distort 23.12.2 Analogue circuits the wanted signal, but if the circuit remains linear in the presence of interference then it may be filtered out in a later stage without ill Analogue circuits are also capable of unexpected oscillation at radio effect. Thus, any circuit which has a good dynamic range and a high frequencies. Gain stages should be properly decoupled, loaded and overload margin will also be relatively immune to interference. 20dB/decade 40dB/decade Figure 23.23 Harmonic spectrum of a trapezoidal waveform: (a) waveform; (b) harmonic spectrum envelope 23/18 Safety and EMC 23.12.3 Software Incident electromagnetic wave Microprocessor circuits with resident embedded software should use all the available software techniques to overcome likely data corruption. This will be due primarily to transients, but also to RFI. Absorption loss A These are: Re-reflection loss B Incorporation of a watchdog timer. Any microprocessor with- out some form of watchdog is inviting disaster when it is exposed to disruptive transients. Reflection loss R 2. Type checking and range checking all input data to determine its reliability. If it is outside range, it should be rejected. Transmitted wave 3. Sampling the input data several times and either averaging it, for analogue data, or acting only on two or three successive identical logic states, for digital data, which is similar to digital Figure 23.24 Losses due to a solid conducting barrier switch de-bouncing. 4. Incorporating parity checking and data checksums in all data transmission. 5. Protecting data blocks in volatile memory with error detecting and correcting codes. How extensively this protection is used (23.7) depends on allowable time and memory overheads. 6. Wherever possible relying on level triggered rather than edge The reflection loss depends on the ratio of wave impedance to triggered interrupts. barrier impedance, the barrier impedance being a function of its 7. Not assuming that programmable interface ch