Month: May 2023

R-2R DAC Getting Popular Over Delta-Sigma ADC

R-2R DACs and Delta-Sigma DACs are two popular types of digital-to-analog converters with distinct advantages and disadvantages.

Delta-Sigma DACs are more popular than R-2R DACs for a few reasons:

  1. Better performance: Delta-Sigma DACs can achieve higher resolution and lower distortion than R-2R DACs, making them better suited for applications that demand high accuracy and fidelity, such as high-end audio.

  2. Lower cost: Delta-Sigma DACs are widely used in consumer electronics, which has driven down the cost of manufacturing and made them more affordable than R-2R DACs in many cases.

  3. Lower power consumption: Delta-Sigma DACs typically consume less power than R-2R DACs, making them well-suited for battery-powered devices.

  4. Greater design flexibility: Delta-Sigma DACs offer greater design flexibility than R-2R DACs, as they can be implemented using a variety of architectures and can be optimized for different performance parameters depending on the application.

One of the key advantages of an R-2R DAC is its simplicity and linearity. R-2R DACs use a resistor network to convert digital data into analog signals, making them easy to design, manufacture and operate. This results in highly accurate, predictable and linear output signals, which are essential for applications such as audio, video, and measurement equipment. Additionally, R-2R DACs are relatively immune to jitter, noise and other digital signal distortions.

There are some recent improvement in R-2R technology such as  the Soekris Discrete R-2R Sign Magnitude Technology

R-2R DACs may be more popular in certain specialized applications, particularly those that require high linearity and accuracy, such as high-end audio equipment. R-2R DACs have a simpler architecture than Delta-Sigma DACs, which can result in better linearity and lower noise, making them better suited for such applications.

In summary, the advantage of R-2R DACs lies in their simplicity and linearity, while Delta-Sigma DACs excel in noise shaping and dynamic range. The choice between the two types of DACs ultimately depends on the specific application requirements and trade-offs between accuracy, speed, resolution, and cost.

What is R-2R DAC

R-2R DAC (Digital-to-Analog Converter) is a type of DAC architecture that uses a network of resistors to convert digital signals into analog signals. It is named after the two types of resistors used in the network: “R” denotes the equal value resistors and “2R” denotes the double value resistors.

In an R-2R DAC, the input digital signal is first converted into binary format and then applied to the resistor network. Each bit of the digital signal is connected to an individual resistor. The values of these resistors are chosen in such a way that the voltage output at the end of the resistor network is proportional to the input digital signal. By adjusting the values of these resistors, the resolution of the DAC can be increased.

One advantage of R-2R DACs is their simplicity and linearity, which makes them well suited for high-performance audio applications. However, they can be more expensive and less power-efficient than other types of DACs, such as Delta-Sigma DACs.

Here is an example of simple 3 bit R-2R DAC circuit.

What is Delta Sigma DAC

Delta-Sigma DAC (Digital-to-Analog Converter) is a type of DAC architecture that uses a technique called delta-sigma modulation to convert digital signals into analog signals. This technique is based on oversampling the input signal at a high rate and then using a feedback loop to filter out the noise and reconstruct the analog signal.

In a delta-sigma DAC, the input digital signal is first oversampled at a very high frequency. The oversampled signal is then filtered using a digital filter that removes the noise and distortion. The resulting signal is then converted to an analog signal using a simple low-pass filter.

Delta-Sigma DACs offer several advantages over other types of DACs. They provide a high signal-to-noise ratio, which means that the output signal is very clean and free from noise and distortion. They are also very power-efficient, as they can be implemented using digital circuitry. However, they may be more complex and less linear than other types of DACs, such as R-2R DACs. Delta-Sigma DACs are commonly used in audio and digital communication systems, where high-quality output and low power consumption are critical.

Example of R-2R DAC

One example of an R-2R DAC that is commonly used in high-performance audio applications is the Burr-Brown PCM1704. This 24-bit DAC features a resistor ladder network that enables highly accurate and linear digital-to-analog conversion, making it well-suited for high-end audio applications. The PCM1704 has a dynamic range of over 120dB and a THD+N (total harmonic distortion plus noise) of -110dB, making it a popular choice among audiophiles and audio equipment manufacturers. The DAC is often used in high-end digital-to-analog converters, preamplifiers, and other audio equipment where accuracy and linearity are critical.

Block diagram of PCM1704 DAC

PCM1704 is already obsolete. For new products, we can use other DAC such as DACx1001 from Texas Instruments

R-2R DAC is used in some high-end audio devices, such as SE300 from Astell & Kern.

Also  Hiby RS8

Example of Delta Sigma DAC

One example of a Delta-Sigma DAC that is commonly used in high-performance audio applications is the ESS Sabre ES9038PRO. This 32-bit DAC uses a multi-bit Delta-Sigma architecture that enables high-precision digital-to-analog conversion with very low noise and distortion. The ES9038PRO is designed for use in high-end audio equipment and has a dynamic range of 140dB and a THD+N of -122dB, making it one of the best performing Delta-Sigma DACs on the market. The DAC is often used in high-end digital-to-analog converters, headphones amplifiers, and other audio equipment where high resolution and low noise are critical.

Here is a typical usage of ESS ES9038PRO

References

 

Advantages of FPGAs Over Microprocessors

FPGAs (Field Programmable Gate Arrays) and microprocessors are both types of digital electronic components, but they have different architectures and are suited to different types of applications. Here are some advantages of FPGAs over microprocessors:

  1. Parallel Processing: FPGAs are designed to perform multiple operations in parallel, which makes them faster than microprocessors for certain types of applications. While microprocessors execute instructions sequentially, FPGAs can perform many operations simultaneously, which is particularly useful for applications that require high-speed data processing or real-time signal processing.

  2. Customizability: FPGAs are highly customizable, allowing users to design custom logic circuits and interfaces for specific applications. In contrast, microprocessors are designed for general-purpose computing and typically require additional hardware components to interface with specialized devices or sensors.

  3. Low Power Consumption: FPGAs can be designed to consume very low amounts of power, making them ideal for battery-powered applications or devices that need to operate in remote or inaccessible locations. Microprocessors, on the other hand, consume more power due to their sequential processing architecture.

  4. High Reliability: FPGAs are less susceptible to software bugs and security vulnerabilities than microprocessors, which can be vulnerable to viruses, malware, and other attacks. This is because FPGAs are configured using hardware descriptions, which are less prone to coding errors and other types of software-related issues.

  5. Real-Time Processing: FPGAs are designed for real-time processing applications, where data processing needs to be done in real-time without delays. Microprocessors, on the other hand, are not optimized for real-time processing and can experience delays due to the nature of their sequential processing architecture.

Relationship between system flexibility and processing performance in specific applications. Positioning of general purpose CPU, GPU, ASIC accelerators and FPGA. From https://hacarus.com/tech/20201207-amd-acquires-xilinx/

Comparison between flexibility and performance of CPU, GPU, FPGA dan ASIC. From: https://www.cs.cornell.edu/courses/cs6120/2022sp/blog/chlorophyll/

Illustration from “Lowest-Power Multi Core RISC-V SoC FPGAs“. Microchip has a comparison of its own microprocessors and FPGAs.

FPGA vs Arm Cortex-A9 vs Arm Cortex-A53

The EEMBC CoreMark-Pro benchmark graph clearly demonstrates the power-efficient nature of the PolarFire SoC FPGA. Leveraging the proven and renowned PolarFire FPGA architecture, the PolarFire SoC delivers exceptional performance with up to 50% lower power consumption than similar FPGAs. Remarkably, the PolarFire SoC FPGA consumes just 1.3W while delivering an impressive 6,500 CoreMarks, outperforming competing SoC FPGAs that deliver no CoreMarks. Moreover, at 8,000 CoreMarks, PolarFire SoC FPGAs consume 55% less power than competing FPGAs. The PolarFire SoC FPGA’s power efficiency combined with its exceptional performance, makes it a go-to choice for power-sensitive applications that demand high performance.

In summary, FPGAs are faster, highly customizable, consume less power, more reliable, and well suited for real-time processing applications compared to microprocessors. However, FPGAs are generally more expensive and require specialized knowledge and tools for programming and configuration. The choice between FPGA and microprocessor will depend on the specific requirements and constraints of the application.

References

Real Time System Without Real Time Operating System

Is it possible to build a real time system without using real time operating system (RTOS)?

Technically it is possible to build a real-time system without using a real-time operating system (RTOS), but it can be more challenging and requires careful design and implementation.

In a real-time system without an RTOS, the software is typically designed to use interrupts and timers to handle events and inputs with specific timing requirements. The code must be carefully structured and optimized to minimize processing time and ensure that critical tasks are executed on time.

There are some alternative to build a real-time system without RTOS include:

  • Cyclic executive. Cyclic executive is a simple scheduling technique that is suitable for small and relatively simple systems with fixed and predictable requirements. In a cyclic executive, tasks are scheduled to run in a fixed order, with each task being given a specific time slice in each cycle. Cyclic executives are easy to implement, but they have limited flexibility and scalability. They may not be suitable for larger or more complex systems with dynamic requirements or varying priorities.
  • Bare-metal programming. This involves writing code directly for the microcontroller or processor without using an operating system. This approach can be fast and efficient, but it requires a deep understanding of the hardware and low-level programming skills.
  • Cooperative multitasking; In this approach, tasks are scheduled to run cooperatively, meaning that they voluntarily yield the processor to other tasks when they are done. Cooperative multitasking can be simpler than using an RTOS, but it may not be suitable for systems with strict timing requirements or tasks with different priorities.
  • Interrupt-driven programming; This approach uses interrupts to handle events and perform tasks, instead of relying on a scheduler. Interrupt-driven programming can be fast and efficient, but it may be more difficult to maintain and debug.

One approach is to use a bare-metal firmware, which is a minimal software layer that provides basic hardware abstraction and implements the real-time behavior directly in the code. Bare-metal firmware can be highly optimized for specific hardware and real-time requirements and can provide fast and predictable performance.

If a full RTOS is to big for our application, another approach is to use a small RTOS which is also known as lightweight real-time kernel or scheduler. Lightweight real-time kernel is a simplified version of an RTOS that provides basic scheduling and synchronization capabilities without the overhead of a full RTOS. Lightweight kernels can be easier to implement than full RTOSes and can be a good compromise between real-time capabilities and simplicity.

Some popular examples of lightweight real-time kernels include:

  1. FreeRTOS: FreeRTOS is a popular open-source LWKernel that is widely used in embedded systems. It provides a small set of kernel services, including task scheduling, synchronization primitives, and inter-task communication.

  2. uC/OS-II: uC/OS-II is a commercial LWKernel that provides a small set of real-time services, including task management, semaphores, and message queues. It is widely used in industrial and medical applications.

  3. ChibiOS/RT: ChibiOS/RT is an open-source LWKernel that is designed for small embedded systems. It provides a small set of kernel services, including task scheduling, synchronization primitives, and inter-task communication.

  4. RIOT: RIOT is an open-source LWKernel that is designed for low-power wireless embedded systems. It provides a small set of kernel services, including task scheduling, synchronization primitives, and inter-task communication.

FreeRTOS logo in green color
FreeRTOS logo

However, using an RTOS can provide many benefits in terms of ease of development, code reusability, and scalability. An RTOS can provide a standardized and well-tested framework for real-time system development and can make it easier to manage complex systems with many tasks and inputs. Ultimately, the choice of real-time system architecture depends on the specific requirements and constraints of the system being developed.

Glossary

  • Bare metal application is a firmware application intended to run without an operating system (OS)
  • A real-time system is a system that must respond to events or inputs within specific time constraints.
  • Operating Systems is a program that control the execution of application programs, and acts as an interface between applications and the computer hardware [Stallings, 2018]
  • A real-time operating system is any operating system that provides a deterministic way of executing a given piece of code. [Stallings, 2018]

References