Mixed-Signal Design Blogs

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The low-power format, CPF/UPF/IEEE1801, has been very popular in the digital simulation world for over ten years. Nowadays, it is also commonly used in the mixed-signal simulations.

Besides the key technologies, such as power shut off, dynamic domain voltage, isolation, level-shifter, etc., there are other two critical components for the low power mixed-signal simulations, power-aware connect modules and mixed-signal power network.

What are these? Let me explain these with the help of figures.

Power-Aware Connect Module

This figure shows how a power-aware connect module (L2E_LPS) converts a power-aware digital signal into an analog signal. In a low-power mixed-signal simulation, the digital blocks (for example, here digital_A) are usually defined in a power domain (PD1) whose power supply voltage and status are described in a low-power format, such as IEEE1801. In the IEEE1801 file shown in this example, two supply sources are described for this block, VDD1 and VDD2. An implicit switch cell is also described in the file to switch between the two sources dynamically. The L2E_LPS connect module is aware of the dynamic switching so that the correct reference voltage is used to convert a logic signal to analog. For example, when logic 1’b1 is converted to analog, at the same time there will be a supply of 1.8V from VDD1 to digital_A. So, the logic 1’b1 will be converted to 1.8V. The next time when 1’b1 is converted again, but with a supply of 1.2V from VDD1 to digital_A, 1’b1 will be converted to 1.2V.

Low-Power Mixed Signal Power Network

This figure shows how a low-power mixed-signal power network works for a mixed-signal simulation. For a large System on a Chip (SoC) design, power intent and power network are usually defined and designed independent of the design configuration, and mostly in the low-power format like IEEE1801. When the SoC is configurated in a mixed-signal scenario, the power network needs to connect natively with both, analog and digital supply sources, and should also be able to distribute the power to both analog and digital function blocks. For example, in the figure above, the Power_Supply module is an electrical modeling block, so the port is providing an electrical signal. This module needs to connect to the power network in the yellow box and then the power supply with the switch cell needs to distribute the power to both the analog_A and digital_B blocks. Not only a static value but the transient change of supply voltage should also be reflected in the supply port of analog_A and digital_B. In this case, a mixed-signal simulation can always run correctly no matter which blocks are configured in analog or digital.

Combined with other low power features, power-aware connect modules and low power mixed-signal power network will help designers to efficiently establish the mixed-signal configuration with their low power specification.

For detailed use model and examples, refer to the low power mixed-signal simulation RAK, Verification of the Power Intent of a Mixed Signal SoC.

~ Qingyu Lin

Related Resources

• One-Stop Knowledge Resource for Mixed-Signal Verification
• Spectre AMS Designer Product Page

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About Start Your Engines

The Start Your Engines! series brings you blog posts from several analog/mixed-signal subject matter experts on a variety of topics, such as introduction to the new features in Spectre AMS Designer, tips for enhanced understanding of existing features, and much more. To receive notifications about new blogs in this series, click Subscribe and submit your email ID in the Subscriptions box.