Designing Voltage Translation in Mixed-Signal Systems

Created: January 1, 2026

Voltage translation or level shifting is normally used with digital signals, often designed for a specific interface without reducing overall channel bandwidth. With huge growth in the number and diversity of ASICs operating at different logic levels, voltage translation has become an essential feature for connecting diverse groups of components. At the system level, many times voltage translators are used which correspond to a specific interface that could operate at different voltages, such as I2C or SPI.

At the circuit level for FPGA developers or ASIC developers, level shifting could be implemented on-chip but only through some available logic gates or analog circuitry on-die. In a CPLD or mixed-signal processor, voltage translation can also be implemented within the available logic cells. This article outlines the typical methods which could be implemented in these types of components.

Fundamental Circuit Techniques for Voltage Translation

At the lowest level, all voltage translators reduce to a small set of circuit designs. Choosing the right one depends on the required directionality, signal edge rate, and noise margin, not just the voltages.

Although most commonly discussed with digital signals, voltage translation can be used with analog signals, essentially changing the amplitude of the signal to comply with a specific interface. The common digital and analog use cases are listed below.

Circuit	Type	Typical Use Cases
Passive translation	Analog	Analog signal translation for an ADC
Op-amp translation	Analog	Analog signal translation with filtering
BJT or MOSFET amplifier	Mixed-signal	Unidirectional control signals
BJT common-emitter	Digital	Unidirectional control signals
MOSFET bidirectional	Digital	I²C, SMBus, alert lines
MOSFET unidirectional	Digital	Push-pull isolation with level shifting
Schmitt trigger or comparator driving	Digital	Logic regeneration for fast edge rates
Logic gate-based translation	Digital	Logic processing and voltage translation simultaneously

Any of these could be implemented with discrete components (such as custom amplifier designs) or with ASICs. For example, voltage translator ICs that are rated to work with push-pull logic or open drain logic (SPI or I2C, respectively) are most common. In some cases, voltage translation is also performed with interface conversion, although these components are more complex and rely on additional circuitry not listed in the above table.

When implemented in an FPGA, CPLD, or mixed-signal processor, the logic gate translation, Schmitt trigger, or comparator approaches are most common. For analog signals, typically an op-amp provides the best control over output voltage (by applying gain in the feedback loop) and current (i.e., with a voltage follower).

Circuit Examples For Voltage Translation

While there are many options for voltage translation, the two examples below show what can be implemented in CPLDs, mixed-signal processors, or FPGAs without built-in level shifting IP.

The example below uses a pair of 2-input NAND gates to step down a signal to a lower voltage (V1 > V2). The resistor forms a voltage divider that steps down the V1 signal to a level that triggers the HIGH/LOW logic states for the V2 gate. The output NAND gate then outputs at a voltage of V2. This example will ensure fast transitions which will only be limited by the switching speed of the output NAND gate. Note that there will be some additional logic propagation delay due to the resistor divider slowing down charging of the input capacitance on the output NAND gate.

The above example could be implemented in any programmable processor which contains these gates, although other gates could also be used. It can also be made bidirectional by placing another cascaded gate arrangement in the opposite direction.

The next example uses a comparator to step an input logic signal up to a higher level (V1). The resistor divider is used to set the threshold voltage. The hysteresis window then provides a narrow undefined region between the HIGH logic output and LOW logic output. The translator will provide non-inverting logic. This example can also be made bidirectional to step up the output either by applying a DC offset on the output or by taking advantage of the fact that comparators can accept inputs which are higher than the supply voltage.

For analog signals, shifting with an op-amp is the best option, which is available in mixed-signal processors. Unfortunately, CPLDs and FPGAs do not include this feature in their programmable blocks, so there will not be any analog processing available on the chip. Everything would need to be done with external discrete components.

For analog signals, a simple op-amp circuit is good enough for voltage translation. Op-amps are the workhorses of analog circuits, and for voltage scaling, an op-amp circuit will be the most robust option. There are two options to use op-amps for voltage translation of an analog signal:

A non-inverting op-amp can be configured to provide gain >1
Use a voltage follower built from a non-inverting op-amp (gain = 1) and step down the input signal with voltage divider
Use an inverting op-amp with either gain or attenuation, and use an inverter on the output if needed

Applications in Mixed-Signal Processors

A mixed-signal processor like Renesas GreenPAK is unique because it allows a designer to implement logic and analog translation in the same chip, including for custom logic interfaces and general-purpose analog. Designers can incorporate both analog sensing and digital data processing in the same chip. This makes programmable mixed-signal processors a highly-integrated platform for a variety of applications that can benefit from on-chip voltage translation:

Power sequencing and monitoring
Multi-interface level shifting
Multi-sensor (digital + analog) interface
Multi-voltage reset control
Consolidation of multiple discrete logic ICs
Digital control in power systems

With Renesas GreenPAK, designers can build these custom ASICs into a single chip thanks to built-in reprogrammable mixed-signal blocks. This brings CPLD-like custom logic and fully customizable analog circuitry into the same programmable component. To help designers build their custom components, Renesas provides the Go Configure Software Hub for configuring programmable logic cells, customizing the component pinout, and designing a fully-integrated analog front-end for analog signal processing.

For applications requiring an op-amp consider the AnalogPAK line of components, which are part of the GreenPAK family. AnalogPAK components are also programmable processors but with additional programmable op-amp blocks for more specialized analog signal processing. An example feature diagram for part number SLG47004 is shown below.

To learn more, take a look at the GreenPAK components and reference examples.

Whether you need to build reliable power electronics or advanced digital systems, use the complete set of PCB design features and world-class CAD tools offered by Altium to implement your GreenPAK solutions. Altium provides the world’s premier electronic product development platform, complete with the industry’s best PCB design tools and cross-disciplinary collaboration features for advanced design teams. Contact an expert at Altium today!