NE567 Tone and Frequency Decoder

Overview

The NE567 (and its SE567 variant) is a highly stable phase-locked loop (PLL) tone and frequency decoder designed for detecting the presence of a specific frequency within its detection band. This integrated circuit is widely used in applications requiring precise frequency detection, such as tone decoding, remote control systems, and communication equipment. The NE567 features synchronous AM lock detection and power output circuitry, enabling it to drive a load when a sustained frequency within its operational bandwidth is detected at its self-biased input.

Features

• Wide Frequency Range: Operates from 0.01Hz to 500kHz, making it suitable for a broad spectrum of applications.
• High Stability of Center Frequency: Ensures reliable and consistent performance over time and temperature variations.
• Independently Controllable Bandwidth: Bandwidth can be adjusted up to 14% of the center frequency, allowing for flexible design configurations.
• High Out-Band Signal and Noise Rejection: Minimizes false triggering from unwanted signals or noise outside the detection band.
• Logic-Compatible Output: Features a 100mA current sinking capability, making it compatible with TTL and CMOS logic circuits.
• Inherent Immunity to False Signals: Designed to reject spurious signals, ensuring accurate frequency detection.
• Frequency Adjustment: Center frequency can be adjusted over a 20-to-1 range using an external resistor.

Applications

The NE567 is versatile and finds use in a variety of electronic systems, including:

• Tone Decoding: Detects specific audio tones in communication systems, such as DTMF decoding.
• Remote Control Systems: Used in infrared or RF remote controls to decode carrier frequencies.
• Telecommunication: Frequency detection in modems and other telecommunication devices.
• Security Systems: Alarm systems that rely on tone detection for triggering.
• Industrial Automation: Frequency-based sensor signal processing.
• Audio Processing: Filtering and detection of specific audio frequencies in sound equipment.

Electrical Characteristics

The following table summarizes the key electrical characteristics of the NE567 under typical operating conditions (unless otherwise specified):

Absolute Maximum Ratings

• Supply Voltage (V+): 10V
• Input Voltage: ±5V
• Output Sink Current: 100mA
• Operating Temperature Range: 0°C to +70°C (NE567), -55°C to +125°C (SE567)
• Storage Temperature Range: -65°C to +150°C

Typical Operating Characteristics

• Center Frequency Range: 0.01Hz to 500kHz
• Bandwidth Adjustment Range: Up to 14% of center frequency
• Input Signal Level for Detection: Typically 20mV RMS
• Output Delay: Adjustable via external components
• Power Supply Current: 7mA typical at V+ = 5V

Package Information

The NE567 is available in multiple package options to suit different application requirements. The following are the most common packages:

8-Pin DIP (Dual Inline Package)

• Package Code: D
• Dimensions: 9.81mm x 6.35mm
• Pin Count: 8
• Material: Plastic

8-Pin SOIC (Small Outline Integrated Circuit)

• Package Code: M
• Dimensions: 5mm x 4mm
• Pin Count: 8
• Material: Plastic

Pin Configuration

The pinout for the NE567 in an 8-pin package is as follows:

• Pin 1: Ground (GND)
• Pin 2: Filter Capacitor (C1)
• Pin 3: Input (Signal In)
• Pin 4: V+ (Positive Supply Voltage)
• Pin 5: Timing Resistor (R1)
• Pin 6: Timing Capacitor (C2)
• Pin 7: Output (Open Collector)
• Pin 8: Bandwidth Adjust (R2)

Functional Description

The NE567 operates as a phase-locked loop (PLL) with an internal voltage-controlled oscillator (VCO), phase detector, and output amplifier. When an input signal within the detection bandwidth is applied, the PLL locks onto the signal, and the output transistor switches to a low state. The center frequency of the detection band is set by an external resistor and capacitor connected to pins 5 and 6, while the bandwidth is adjusted using a resistor connected to pin 8.

Key Functional Blocks

• Voltage-Controlled Oscillator (VCO): Generates a frequency determined by external timing components.
• Phase Detector: Compares the input signal phase with the VCO output phase to generate an error signal.
• Amplifier and Filter: Processes the error signal to control the VCO and provide lock detection.
• Output Stage: An open-collector transistor that sinks current when the input frequency is within the detection band.

Design Considerations

When designing with the NE567, the following factors should be considered to ensure optimal performance:

• Center Frequency Selection: The center frequency (f0) is determined by the external resistor (R1) and capacitor (C2) connected to pins 5 and 6, respectively. The formula for f0 is approximately f0 ≈ 1.1 / (R1 × C2).
• Bandwidth Adjustment: The detection bandwidth is set by the resistor connected to pin 8 (R2) and is typically 7% of f0 per kΩ of R2.
• Input Signal Level: The input signal should be at least 20mV RMS for reliable detection. Excessive input levels may cause false triggering.
• Power Supply Decoupling: A 0.1µF capacitor should be placed close to the V+ pin (pin 4) to minimize noise and ensure stable operation.

Conclusion

The NE567 is a versatile and reliable tone and frequency decoder suitable for a wide range of applications. Its ability to detect specific frequencies with high stability and adjustable bandwidth makes it an excellent choice for designers working on communication, control, and audio systems. By carefully selecting external components and following design best practices, the NE567 can deliver robust performance in even the most demanding environments.