BLK_SlewrateDriver : A slew-rate controlled driver

A slew-rate controlled driver converts a digital input in to an analog output out with variable slew rates for rising and falling transitions, controlled by the SR_rise and SR_fall inputs, respectively. In other words, it has a similar functionality to the transition primitive, except that its rise and fall times can be varied with the signals.

The slew rate inputs SR_rise and SR_fall define the respective slew rates in units of V/ns. The parameters value0 and value1 define the analog output values corresponding to the logic-0 and logic-1 values of the digital input, respectively. The parameter scale defines the additional scale factor that can be applied to the slew rate inputs.

This slew-rate controlled driver model is described using a pair of switched current sources charging/discharging a capacitor. For example, the ratio between the charging current (iup) and capacitance determines the slew rate for the rising transition. The capacitor is modeled with the cap_var primitive, which has a 1nF capacitance in the mid range but has infinite capacitance when its voltage reaches value1 or value0. This is a handy way of saturating the output out at the levels of value1 and value0.

Input/Output Terminals

Name	I/O	Type	Description
out	output	xreal	analog output
SR_fall	input	xreal	falling slew rate (V/ns)
SR_rise	input	xreal	rising slew rate (V/ns)
in	input	xbit	digital input

Parameters

Name	Type	Default	Description
value0	real	0.0	value for logic 0
value1	real	1.0	value for logic 1
scale	real	1.0	scale factor for slew rate

List of Testbenches

tb_check_fixedfreq : A testbench for checking the operation of a slew-rate controlled driver with a fixed-frequency input

tb_check_varfreq : A testbench for checking the operation of a slew-rate controlled driver with a variable-frequency input

tb_check_fixedfreq : A testbench for checking the operation of a slew-rate controlled driver with a fixed-frequency input

This testbench checks the basic functionality of a slew-rate controlled driver by feeding a fixed-frequency digital data as the input and slowly varying one of the slew rate input SR_rise. The expected output is an analog output with finite rise and fall times where the rise time slowly varies over time.

Simulation Results

tb_check_varfreq : A testbench for checking the operation of a slew-rate controlled driver with a variable-frequency input

This testbench checks the basic functionality of a slew-rate controlled driver by feeding a digital clock with a slowly-varying frequency as the input. The slew rates of both the rising and falling transitions are controlled so that the rise and fall times occupy a constant fraction of the clock period. The expected output is an analog clock whose rise and fall times scale proportionally with the clock period.

Simulation Results