Digital-to-Analog Node Bridge

The dac_bridge is the first of two node bridge devices designed to allow for the ready transfer of digital information to analog values and back again. The second device is the adc_bridge (which takes an analog value and maps it to a digital one).

The dac_bridge takes as input a digital value from a digital node. This value by definition may take on only one of the values "0", "1" or "U". The dac_bridge then outputs the value "out_Low", "out_high" or "out_undef", or ramps linearly toward one of these "final" values from its current analog output level. The speed at which this ramping occurs depends on the values of "t_rise" and "t_fall". These parameters are interpreted by the model such that the rise or fall slope generated is always constant.

Note: Note that the dac_bridge includes test code for determining the presence of the out_undef parameter. If this parameter is not specified by you, and if out_high and out_low values are specified, then out_undef is assigned the value of the arithmetic mean of out_high and out_low. This simplifies coding of output buffers, where typically a logic family will include an out_low and out_high voltage, but not an out_undef value.

This model also posts an input load value (in farads) based on the parameter input_load.

Port Table

Description Direction Default Type Allowed Types Vector Vector Bounds Null Allowed
Input IN d d YES   NO
Output OUT v v,vd,i,id YES   NO

Parameter Table

Name Description Data Type Default Value Limits Vector Vector Bounds Null Allowed
out_low analog output for 'ZERO' digital input Real 0.0   NO   YES
out_high analog output for 'ONE' digital input Real 1.0   NO   YES
out_undef analog output for 'UNDEFINED' digital input Real 0.5   NO   YES
input_load capacitive input load (F) Real 1.0e-12   NO   YES
t_rise rise time 0 -> 1 Real 1.0e-9 1e-12 / - NO   YES
t_fall fall time 1 -> 0 Real 1.0e-9 1e-12 / - NO   YES


abridge1 7 2 dacl
.model dacl dac.bridge(out.low = 0.7 out.high = 3.5 out.undef = 2.2 
+                      input_load = 5.Oe-12 t.rise = 50e-9 f.fall = 20e-9)

See also

XSPICE Devices
XSPICE Code Models