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Simulator Reference Manual Model parameters Name Description Type Default Limits in_low Maximum 0-valued analog input real 0.1 none in_high Minimum 1-valued analog input real 0.9 none rise_delay Rise delay real 1nS 1e-12 - ∞ fall_delay Fall delay real 1nS 1e-12 - ∞ time_tol Threshold time tolerance real 100pS 1e-12 - ∞ out_low Used to calculate reflected static load. See text real 0 none out_high Used to calculate reflected static load. See text real 5 none clamp_low Clamp threshold 'ZERO' digital input. Default to out_low real out_low none clamp_high Clamp threshold 'ONE' digital real input. Default to out_high out_high none clamp_res Clamp minimum resistance real 1 1e-06 - ∞ clamp_bias Clamp voltage real 0.8 0.2 - 2 out_family Output logic family string UNIV none Device Operation The analog-digital interface bridge is the main device used to connect analog signals to digital inputs. The device produces a digital signal that is in the logic '1' state when the analog input is above the high threshold (IN_HIGH) and a logic '0' state when it is below the low threshold (IN_LOW). When the analog input is in between these two states the output will be in the UNKNOWN state. The changes in state will be delayed according to the RISE_DELAY and FALL_DELAY parameters. Analog input load The analog input presents a load to its driving circuit according to the digital load that is being driven. In other words the digital load is reflected to the analog input. Both static (i.e. DC) and dynamic (i.e. capacitance) elements of the load are reflected. To accurately reflect the sink and source currents, the interface bridge needs to know the voltage levels of the device it is driving. The digital device will (usually) have a SINK_CURRENT and a SOURCE_CURRENT model parameter each of which apply at defined logic voltage levels. These levels must be specified in the OUT_LOW and OUT_HIGH parameters of the AD interface bridge model. The input is modelled by a current source in parallel with a resistor. The values of these components are calculated from the above mentioned parameters and the digital load. 154
