Source: Tiger Says Chip
Original Author: Tiger Says Chip
This article mainly discusses the basic concepts of DAC chips, working principles, common architectures, performance metrics, design challenges, manufacturing processes, and typical applications.
What is a DAC Chip?
A DAC, or Digital-to-Analog Converter, is also known as a Digital-to-Analog Converter. Its function is to convert digital signals (binary codes composed of 0s and 1s) into analog signals (continuous physical signals such as voltage and current). In simpler terms, a DAC chip is essentially the “announcer” that bridges the digital world to the analog world.
For example, an ADC is like a microphone that converts your spoken words into digital data for a computer; a DAC is like a speaker that converts the “0101” data back into sounds you can understand.
In summary: A DAC is the exit for digital systems to the analog world..
Why are DAC Chips Important?
Various electronic products we use, especially output devices like speakers, displays, motor controllers, and power controllers, almost all need to output the calculated “digital signals” as “perceptible analog signals” in the real world.
Here are a few examples to illustrate:
Mobile audio: Digital music is converted into electrical signals through a DAC to drive the speakers;
Display systems: Digital image data is converted into analog voltage through a DAC to control the brightness of LCD pixels;
Industrial control: The control quantities calculated by PLCs are output as voltage or current through a DAC to drive motors or actuators.
In summary: Without a DAC, digital chips cannot truly “speak” or “exert force”.
The Basic Principle of DAC: How to Convert 0s and 1s into Continuous Voltage?
The core idea of a DAC is: to correspondingly map discrete digital codes to analog quantities (usually voltage or current)..
An N-bit DAC can output 2ⁿ different analog levels. For example, an 8-bit DAC can output a maximum of 256 different voltages, a 12-bit DAC can output 4096, and a 16-bit DAC can output 65536.
The working process is mainly divided into three stages:
Receiving Digital Input: The digital logic module provides a fixed-length binary data (e.g., 10110011);
Converting to Analog Quantity: The internal circuits of the DAC generate a corresponding voltage/current based on the digital code under a reference voltage (Vref);
Outputting Analog Signal: The voltage or current is sent to the subsequent circuit through the output port, such as amplifiers, motor control, LED drivers, etc.
The key question is “how to convert”: common structures include resistor networks, current source arrays, capacitive dividers, charge pumps, etc.
Common DAC Structures: Each “Broadcasting Method” Has Its Own Merits
1.Resistor Ladder (R-2R DAC)
Principle: A voltage divider network composed of equal proportions of R and 2R resistors is used to achieve weight conversion.
Advantages: Simple structure, easy to implement.
Disadvantages: High precision requirements for resistors, not suitable for high resolution.
Applications: Audio playback, simple control circuits.
2. Current Steering DAC
Principle: Digital codes control multiple current source switches, combining them into different currents, which are then converted into voltage.
Advantages: Fast speed, suitable for high sampling rates.
Disadvantages: Requires precise current source matching, significant manufacturing challenges.
Applications: High-speed communication systems, video, broadcasting equipment.
3. Capacitive DAC
Principle: Uses capacitors of different sizes for voltage division, gradually approaching the target output.
Advantages: High integration, low power consumption, suitable for System on Chip (SoC).
Disadvantages: Accuracy depends on capacitor matching, susceptible to process drift.
Applications: Mobile devices, low-power control systems.
4. Σ-Δ DAC (Sigma-Delta)
Principle: Digital signals are modulated into high-frequency 1/0 sequences, then low-pass filtered into analog signals.
Advantages: High precision, low cost, strong anti-interference.
Disadvantages: High output latency, limited bandwidth.
Applications: High-precision audio, instrumentation, medical devices.
Performance Metrics: The “Health Report” for Evaluating a DAC Chip
1. Resolution (Resolution)
Unit: bit. Represents the number of levels a DAC can distinguish; the higher the resolution, the more “delicate” the output.
2. Update Rate
Unit: SPS (Samples per Second), the speed of output refresh.
Commonly used audio rate is 44.1kHz, while video or radar can reach GHz levels.
3. Linearity (INL/DNL)
INL (Integral Non-Linearity): The overall deviation between actual output and ideal output;
DNL (Differential Non-Linearity): Whether the transitions between each bit are consistent.
4. Output Range and Full-Scale Error
The maximum and minimum voltage range that the output can cover; ideally should match Vref.
5. Noise and Distortion (SNR, THD, SFDR))
Affecting the clarity and dynamic range of audio and signal systems; the higher the SNR, the better.
6. Power Consumption and Supply Voltage
Key metrics for battery-operated devices; most DACs operate in the 1.8V~5V supply range.
Manufacturing Processes and Packaging: Stability is More Important than Advancement
Like ADCs, most DACs are primarily analog circuits with supplementary logic circuits, and their dependence on advanced processes is relatively low.
Process Selection:
Mainstream Processes: Mainly 0.18μm, 0.13μm CMOS;
High-End Applications: Local mixed BiCMOS or 28nm FinFET;
Audio DACs: Particularly focus on noise, PSRR, and other analog characteristics, often using mature processes.
Packaging Methods:
Small Packages: QFN, TSSOP, SOIC, suitable for consumer products;
Large Packages: BGA, LGA, suitable for multi-channel, high-speed DAC applications;
Some DACs are directly integrated into SoCs, FPGAs, or DSP chips, adopting system-in-package (SIP/POP).
Design Challenges: Don’t Underestimate the Depth of DACs
1. Complex Analog Circuit Design
Each bit of precision requires matching resistors, current sources, capacitors, etc.; manufacturing deviations can cause output errors.
2. Linearity and Temperature Drift Control Difficulties
Process drift and temperature changes can easily affect circuit characteristics, requiring temperature compensation and dynamic calibration mechanisms.
3. Power Supply Noise Sensitivity
Power supply ripple, switching interference, etc., significantly impact DAC output, necessitating careful layout and bypass design.
4. High Speed and High Resolution Difficult to Achieve Simultaneously
It is challenging to achieve either high speed (e.g., 1Gsps) or high resolution (e.g., 20-bit) simultaneously.
5. High Testing Costs
Especially when testing multi-channel, high-precision DACs, high-resolution instruments and shielded environments are required.
Application Scenarios: DACs as the “Unsung Heroes” in Various Industries
| Application Field | Typical Uses |
|---|---|
| Audio Systems | Decoder output, speaker drive, headphone amplifier |
| Industrial Control | Voltage output modules, current loops, servo control |
| Instrumentation | Power calibration, sensor drive, oscilloscope bias |
| Communication Systems | RF signal generation, IQ modulation, transmission links |
| Medical Electronics | Heart rate monitoring, electrical stimulation devices, ultrasound probe control |
| Automotive Electronics | Motor control, headlight dimming, electronic dashboards |
| Consumer Electronics | Display control, power regulation, game controller vibration, etc. |
Future Trends: The Demand for Analog Outputs from the Digital World Will Only Increase
1. Stronger Integration
More and more DACs are integrated into SoCs, MCUs, and FPGAs, forming a complete “signal chain closed loop”.
2. Low Power and Small Size
Adapting to miniaturized scenarios such as IoT, wearables, and medical patches.
3. Intelligent and Self-Calibrating
Dynamic temperature drift calibration, tolerance self-adjusting circuits, AI-assisted calibration, etc., are on the rise.
4. High-Speed Multi-Channel Parallel Output
Targeting radar, video streaming, wireless communication, and other multi-antenna scenarios, high-speed multi-channel DACs will become mainstream.
Conclusion: Although DAC Chips Are “Quiet”, Their Contributions Are Indispensable
DAC chips are an essential part of the entire electronic system, serving as the key for digital systems to “communicate” with the real world. From mobile audio to aerospace, from industrial instruments to smart home speakers, DACs are everywhere.
Although digital IC design has received significant attention in recent years, analog chips, especially precision analog devices like DACs, not only have high design thresholds but also long product lifecycles, requiring extensive experience from engineers, making it one of the true fields that reflect “hard power”.
END
Reprinted content only represents the author’s views
Does not represent the position of the Institute of Semiconductors, Chinese Academy of Sciences
Editor: Yi Er
Responsible Editor: Youzi Lu
Submission Email: [email protected]
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