onsemi SA572DR2G: Key Features and Application Circuit Design

The onsemi SA572DR2G is a highly integrated, monolithic Compandor IC, specifically designed for dynamic range compression and expansion in audio systems. Its primary function is to improve the signal-to-noise ratio (SNR) of audio transmission systems, making it a cornerstone component in professional audio equipment, telecommunications, and noise reduction systems.

Key Features

The SA572DR2G stands out due to its sophisticated internal architecture and performance characteristics:

Dual-Channel Operation: The device contains two independent compandor channels in a single package. This allows for stereo signal processing or simultaneous compression and expansion, making it highly efficient for complex audio chains.

High-Signal Handling Capacity: It boasts a wide dynamic range, capable of handling input signals up to 3 Vrms, which minimizes distortion and ensures high-fidelity audio processing.

Low Distortion and Noise: The internal circuitry is optimized for exceptionally low total harmonic distortion (THD) and low noise, preserving audio quality throughout the compression and expansion processes.

Wide Power Supply Range: It operates from a single supply voltage ranging from 6V to 18V, or from dual supplies (±3V to ±9V), offering significant flexibility in different system design configurations.

Temperature Stability: The internal reference circuitry provides excellent temperature stability, ensuring consistent performance across varying environmental conditions.

Space-Efficient Packaging: The SA572DR2G is offered in a compact SOIC-16 package, ideal for space-constrained PCB designs.

Application Circuit Design

A typical application for the SA572DR2G is in a companding system for a wireless microphone or an audio link. The following outlines a basic circuit design for one channel.

1. System Block Diagram:

The complete system utilizes both channels of the IC. One channel is configured as a compressor at the transmitter side, and the other as an expander at the receiver side.

Transmitter (Compression): The audio input signal is compressed. Low-level signals are amplified, and high-level signals are attenuated. This process reduces the dynamic range of the signal before transmission, making it less susceptible to noise introduced by the transmission medium.

Receiver (Expansion): The received signal is expanded, performing the exact inverse function of the compressor. This restores the original dynamic range of the audio signal while simultaneously attenuating any noise picked up during transmission.

2. Basic Compressor Circuit Design (One Channel):

The external component selection is critical for defining the compressor's characteristics.

Input Section: The audio signal is fed into the input pin (e.g., Channel 1 Input) through a DC-blocking capacitor. A resistor to ground sets the input impedance.

Rectifier Filter (Key to Compression): The gain control element is an internal voltage-controlled amplifier (VCA). Its gain is determined by a control voltage derived from the output signal itself. An external capacitor (`C_REC`) connected to the rectifier filter pin sets the attack and release times of the compressor. A larger value results in slower response times, while a smaller value makes the compressor react more quickly.

Output and Gain Setting: The output is taken from the channel output pin, again through a DC-blocking capacitor. The ratio of compression is set by the feedback network around the internal op-amp, typically using precision resistors.

Power Supply Decoupling: It is crucial to place 0.1 µF ceramic decoupling capacitors as close as possible to the power supply pins (V+ and GND) to ensure stable operation and prevent oscillation.

Design Considerations:

Threshold Level: The internal circuitry has a fixed compression threshold. The system's operating level must be designed to align with this threshold for optimal performance.

Noise Floor: Careful PCB layout is essential. Keeping audio traces short, separating analog and digital grounds, and using a solid ground plane help achieve the IC's low-noise potential.

External Component Tolerance: Using components with 1% tolerance or better for resistors and capacitors in the signal and rectifier paths is recommended to ensure channel matching and predictable performance.

ICGOODFIND: The onsemi SA572DR2G remains a classic and robust solution for dynamic range manipulation. Its dual-channel integration, excellent audio performance, and design flexibility make it an ideal choice for engineers developing high-quality audio companding systems, from professional wireless audio links to sophisticated noise reduction modules.

Keywords: Compandor IC, Dynamic Range Compression, Audio Signal Processing, Low Distortion, Application Circuit Design