Cadence Mixed-Signal Circuit Design Environment User Guide
Interface Element Macro Models
October 2003
72
Product Version 5.0
Parameters
D2A_VL D2A_VH
,
D2A_TR
, and
D2A_TF
control the interface primitive
da&1
.
Parameters
D2A_HI_TH
,
D2A_LOW_TH
,
D2A_R1
, and
D2A_R0
control the switching
thresholds and the on-resistance (closed-resistance) of the switches. The off-resistance of
the switches, which are fixed at
1e12
in the model, could have been parameterized.
The interface primitive
da&1
drives an intermediate node
&1
. Instance
X&1
, which
implements a subcircuit containing pull-up and pull-down switches, voltage source, and
capacitance, is connected between the intermediate node and the interface net
&2
.
When a logic 1 is received, the intermediate node rises to
D2A_VH
, which should exceed
D2A_HI_TH
, causing switch
W1
to close and
W2
to open, so the output impedance is at
D2A_R1
.
When a logic 0 is received, the intermediate node falls to
D2A_VL
, which should be below
D2A_LOW_TH
, causing switch
W2
to close and
W1
to open, so the output impedance is at
D2A_R0
.
When a logic Z is received, the output of the interface primitive settles to (
D2A_VL
+
D2A_VH
)/
2, which should be in between
D2A_HI_TH
and
D2A_LOW_TH
, both switches are off, and the
output of the interface element is at high impedance. The user must choose parameters so
that
D2A_LOW_TH
< (
D2A_VL
+
D2A_VH
)/2 <
D2A_HI_TH
.
The switching time observed at the interface net depends on the following three factors:
s
Switching time of the interface primitive
s
Switching time of the pull-up/pull-down switches
&3
D2A_VL
&4
D2A_VH
&5
D2A_TR
&6
D2A_TF
&7
D2A_HI_TH
, switching threshold of pull-up switch
&8
D2A_LOW_TH
, switching threshold of pull-down switch
&9
D2A_R1
, on-resistance of pull-up switch
&10
D2A_R0
, on-resistance of pull-down switch
Macro
Parameter
Mnemonic Parameter Name