Modeling the CD4051 in SPICE: Bridging the Gap Between Datasheet and Simulation
To accurately simulate a CD4051, the model must be decomposed into its functional blocks. A "black box" approach is insufficient for analyzing signal integrity or crosstalk. Therefore, a robust SPICE subcircuit typically models three distinct sections: the digital control decoding logic, the analog switch core, and the parasitic elements.
* Simple CD4051 behavioral model (8:1 mux) .SUBCKT CD4051 COM A0 A2 A1 INH VEE VSS VDD * Add logic decoding + analog switch here .ENDS cd4051 spice model
Hi everyone,
A nuance often overlooked in generic models is the CD4051’s unique supply structure. The device supports a wide voltage range and a separate $V_EE$ pin, allowing it to switch bipolar signals. An accurate SPICE subcircuit must enforce the logic thresholds relative to these supplies. Modeling the CD4051 in SPICE: Bridging the Gap
The heart of the CD4051 model is the analog switch. In the physical silicon, this is implemented using a CMOS transmission gate—a parallel combination of an NMOS and a PMOS transistor. This configuration allows the switch to pass signals across the full voltage range ($V_DD$ to $V_EE$), mitigating the threshold voltage drop associated with single-transistor switches.
But this lacks analog accuracy.
Digital control pins D A A 0 DMOS D B B 0 DMOS D C C 0 DMOS
For example, the digital inputs ($A, B, C$) are referenced to $V_SS$ (logic ground), but the analog signals can swing negative down to $V_EE$. The SPICE model must include level-shifting circuitry to ensure that the digital control signals correctly bias the transmission gates, even when passing negative analog voltages. If a model assumes a single ground reference, it will fail to simulate negative signal passing, rendering it useless for bipolar applications. * Simple CD4051 behavioral model (8:1 mux)
SPICE (Simulation Program with Integrated Circuit Emphasis) is a widely used circuit simulator that allows designers to simulate the behavior of electronic circuits. To create a SPICE model for the CD4051, we need to accurately model its electrical behavior, including its analog and digital inputs, output, and internal switching circuitry.
Or suggestions for modeling it accurately using ideal switches + measured Ron curves?