Push-Pull Output

Behavioral representation of CMOS complementary output stage

Libraries:
Simscape / Electrical / Integrated Circuits

Description

The Push-Pull Output block represents a CMOS complementary output stage behaviorally. To improve simulation speed, the block does not model all the internal individual MOSFET devices that make up the gate. You can use this block to create a representative output current-voltage relationship when defining an integrated circuit model behavior with Physical Signal blocks from the Simscape™ Foundation library.

You can choose between are two output current-voltage relationships:

Linear — The block represents the output as a voltage source plus series resistance and parallel capacitance, as shown in the following figure. The value you specify for the Output resistance parameter is assigned to the series resistance, and the capacitance values are determined by matching the RC time constant to the Propagation delay parameter value.
The input to the Controlled Voltage Source block is limited to be between the supply rails, and it is also inverted by subtraction from the supply voltage. The inversion makes it behave like a complementary output stage, with a high gate-source voltage resulting in a low output.
Quadratic — The output stage is modeled by the two MOSFETs that constitute the complementary pair. The MOSFET parameters are derived from the output resistance values and short-circuit currents that you specify as mask parameters. The gate input demand is lagged to approximate the Propagation delay parameter value.

Both Linear and Quadratic output models add an offset and scale the physical input X so that the gate voltage is given by:

Vg = k · ( X + c )

(1)

where

k is the input signal scaling.
c is the input signal offset.

The offset and scaling can be used, for example, to match logical values for X (that is, range [0,1] ) to [V-, V+] at the output pin. For example, if V+ = 10V and V- = 0, then to match the signal logical values to this voltage range, set c = -1 and k = -10.

For both Linear and Quadratic output models, the protection diodes D1 and D2 act to limit the output voltage range. These diodes are Diode blocks from the Simscape Foundation library, that is, piecewise linear diodes defined by their forward voltage and on resistance. If the voltage across D1 rises above the forward voltage, then the diode starts to conduct, and provided that the on resistance is low, it effectively prevents the output rising above V+ plus the diode forward voltage drop. An equivalent behavior results if the output voltage drops too low.

The output model is very similar to that used for the logic blocks. For a plot of a typical output V-I characteristic when using the Quadratic output model, see Selecting the Output Model for Logic Blocks.

Note

This block is constructed out of blocks from the Simscape Physical Signals library (such as PS Add, PS Gain, and so on). Currently, the blocks in the Physical Signals library do not support unit propagation and checking. For more information, see How to Work with Physical Units.

Examples

Modeling an Integrated Circuit

Two ways to create a model of an integrated circuit that can be used in conjunction with other Simscape™ Electrical™ blocks. The first approach is to build a behavioral model using Simscape Foundation Library PS blocks and/or Simulink® blocks. The second is to build an implementation model from basic Simscape Electrical blocks. To look under the masks and view the details, select the relevant block and type ctrl-U.

Open Model

Assumptions and Limitations

The block does not accurately model dynamic response.
The Quadratic output model does not model any output capacitance effects. Add output capacitance externally to the block if required.

Ports

Input

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X — Input port
physical signal

Physical port associated with the Push-Pull Output input.

Conserving

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J — Output port
electrical

Electrical conserving port associated with the block output. The port name is hidden on the block icon, but you can see it in simulation data logs.

Parameters

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Input Scaling

Input signal scaling, k — Input signal scaling
`1` `V` (default)

The input physical signal X is mapped to the gate voltage by Vg = k · ( X + c ), where k is the input signal scaling. Use this parameter in conjunction with the Input signal offset, c to map the range of X to the voltage range defined by the power supply.

Input signal offset, c — Input signal offset
`0` (default)

The input physical signal X is mapped to the gate voltage by Vg = k · ( X + c ), where c is the input signal offset. Use this parameter in conjunction with the Input signal scaling, k to map the range of X to the voltage range defined by the power supply.

Output Characteristics

Output current-voltage relationship — Output model
`Linear` (default) | `Quadratic`

Select the output model:

Linear - the output voltage drops linearly with output current. This is the default option.
Quadratic - the output voltage dependency on output current is defined by the quadratic I-V characteristics of the two output MOSFET devices.

Output resistance — Output resistance
`25` `Ohm` (default)

Defines one over the slope of the output I-V characteristic.

Dependencies

This parameter is visible only when the Output current-voltage relationship parameter is set to Linear.