NE570N Dual Gain Control Circuit

Overview

The NE570N is a versatile, low-cost dual gain control circuit designed for dynamic range compression or expansion applications. Each channel of this IC includes a full-wave rectifier for signal detection, a linearized temperature-compensated gain cell, and an operational amplifier. The NE570N is widely used in audio processing, telecommunications, and noise reduction systems due to its high dynamic range and flexible configuration options.

Features

• Complete compressor and expandor functionality in a single IC
• Temperature-compensated for stable performance across operating conditions
• Greater than 110 dB dynamic range for high-quality signal processing
• Wide operating voltage range down to 6 VDC
• Adjustable system levels through external components
• Distortion trimming capability for improved signal fidelity
• Dual-channel architecture for stereo or dual-processing applications

Applications

• Cellular radio systems
• Telephone trunk compandors
• High-level limiters
• Low-level expandors (noise gates)
• Dynamic noise reduction systems
• Voltage-controlled amplifiers
• Dynamic filters
• Professional audio equipment
• Broadcast equipment

Electrical Characteristics

Absolute Maximum Ratings

• Maximum operating voltage (VCC): 24 VDC
• Operating ambient temperature range (Tamb): 0°C to +70°C
• Power dissipation (PD): 400 mW

AC Electrical Characteristics

VCC = +6 V, Tamb = 25°C; unless otherwise stated.

• Supply voltage (VCC): 6 V to 24 V
• Supply current (ICC) with no signal: 3.2 mA (typical), 4.8 mA (maximum)

Package Information

Pin Configuration

The NE570N is available in a 16-pin small outline package (SO16) with the following pinout:

• Pin 1: RECT_CAP_1
• Pin 2: RECT_IN_1
• Pin 3: ∆G_CELL_IN_1
• Pin 4: GND
• Pin 5: RECT_CAP_2
• Pin 6: RECT_IN_2
• Pin 7: VCC
• Pin 8: INV_IN_2
• Pin 9: ∆G_CELL_IN_2
• Pin 10: THD_TRIM_2
• Pin 11: OUTPUT_2
• Pin 12: RES_R3_2
• Pin 13: THD_TRIM_1
• Pin 14: OUTPUT_1
• Pin 15: RES_R3_1
• Pin 16: INV_IN_1

Ordering Information

• Type number: NE570D
• Package: SO16 (plastic small outline package)
• Lead count: 16
• Body width: 7.5 mm
• Temperature range: 0°C to +70°C

Functional Description

The NE570N consists of two independent channels, each containing a full-wave rectifier, variable gain cell, and operational amplifier. The rectifier detects the average signal level, which controls the gain cell to either compress or expand the dynamic range. The temperature compensation ensures stable operation across the specified temperature range.

Block Diagram Description

The internal architecture includes:

• Rectifier section for signal level detection
• Variable gain cell for dynamic range control
• Operational amplifier for signal processing
• THD trim adjustment for distortion control
• Reference voltage (VREF) of 1.8 V
• Internal resistors (R1 = 10 kΩ, R2 = 20 kΩ, R3 = 20 kΩ, R4 = 30 kΩ)

Design Considerations

Compressor Configuration

When configured as a compressor, the NE570N reduces the dynamic range of the input signal by decreasing gain as the input level increases. This is particularly useful in applications where signal levels need to be maintained within a specific range.

Expander Configuration

In expander mode, the IC increases the dynamic range by reducing gain for low-level signals (acting as a noise gate) while maintaining higher gain for stronger signals. This configuration is valuable for noise reduction systems.

External Component Selection

The performance characteristics can be adjusted through careful selection of external components:

• Rectifier capacitor values affect attack and release times
• Resistor networks determine compression/expansion ratios
• THD trim adjustments optimize distortion performance

Performance Characteristics

The NE570N offers excellent performance across its operating range:

• Low distortion operation when properly trimmed
• Consistent performance across the 6V to 24V supply range
• Minimal crosstalk between channels
• Stable operation over the full temperature range

Typical Application Circuits

Dynamic Noise Reduction System

When used in noise reduction applications, one channel can be configured as an expander to reduce noise during quiet passages while maintaining full dynamic range during louder passages.

Telephone Compandor

In telephone systems, the NE570N can provide companding (compression at the transmitter and expansion at the receiver) to improve signal-to-noise ratio over the transmission channel.

Conclusion

The NE570N is a highly versatile and cost-effective solution for dynamic range control applications. Its dual-channel architecture, wide operating voltage range, and excellent performance characteristics make it suitable for a wide variety of audio processing and telecommunications applications. The ability to configure each channel independently as either a compressor or expandor provides designers with significant flexibility in system implementation.