LM567V Tone Decoder

Overview

The LM567V and LM567C are general-purpose tone decoder integrated circuits designed to detect the presence of a specific frequency within an input signal. Upon detection, the device provides a saturated transistor switch to ground, making it useful for frequency detection and decoding applications. The circuit comprises an I (in-phase) and Q (quadrature) detector driven by a voltage-controlled oscillator (VCO), which sets the center frequency of the decoder. External components allow for independent configuration of the center frequency, bandwidth, and output delay, providing flexibility in design.

Features

• Wide Frequency Range: Operates across a 20:1 frequency range with the use of an external resistor, allowing for versatile application in various frequency bands.
• Logic-Compatible Output: Features a transistor output capable of sinking up to 100 mA, making it compatible with TTL and CMOS logic circuits.
• Adjustable Bandwidth: External components enable precise control over the detection bandwidth, ensuring accurate frequency discrimination.
• Stable Center Frequency: The voltage-controlled oscillator (VCO) provides a stable and tunable center frequency for reliable tone detection.
• Low Power Consumption: Designed for efficient operation, making it suitable for battery-powered applications.
• High Noise Immunity: The I and Q detector structure enhances noise rejection, reducing false triggering in noisy environments.

Applications

The LM567V is widely used in applications requiring precise frequency detection and decoding. Some common use cases include:

• Tone Decoding: Detecting specific tone frequencies in telecommunication and audio processing systems.
• Remote Control Systems: Used in infrared (IR) and radio frequency (RF) remote controls for command decoding.
• Frequency-Shift Keying (FSK) Demodulation: Decoding FSK signals in data transmission systems.
• Security Systems: Employed in alarm and access control systems for tone-based activation.
• Industrial Automation: Detecting machine status or signaling events based on frequency-encoded signals.
• Ultrasonic Detection: Used in proximity sensors and object detection systems operating in ultrasonic frequency ranges.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM567V under typical operating conditions (unless otherwise noted):

Absolute Maximum Ratings

• Supply Voltage (V_CC): 10V
• Output Sink Current: 100 mA
• Operating Temperature Range: -25°C to +85°C
• Storage Temperature Range: -65°C to +150°C

Operating Characteristics (V_CC = 5V, T_A = 25°C)

• Center Frequency Range: Adjustable from 0.01 Hz to 500 kHz (dependent on external components)
• Detection Bandwidth: Programmable from 1% to 14% of the center frequency
• Input Signal Level: 10 mV to 3 V RMS for reliable detection
• Output Saturation Voltage: ≤ 0.4V at 100 mA sink current
• Supply Current: Typically 7 mA (varies with operating frequency)
• Frequency Stability: ±50 ppm/°C (typical)

Package Information

The LM567V is available in multiple package options to suit different assembly and thermal requirements. The following are the most common package types:

8-Pin DIP (Dual Inline Package)

• Package Code: N
• Dimensions: 9.81 mm x 6.35 mm (0.386 in x 0.250 in)
• Pin Pitch: 2.54 mm (0.100 in)
• Material: Molded Plastic

8-Pin SOIC (Small Outline Integrated Circuit)

• Package Code: D
• Dimensions: 4.90 mm x 3.91 mm (0.193 in x 0.154 in)
• Pin Pitch: 1.27 mm (0.050 in)
• Material: Molded Plastic

Pin Configuration

The pinout for the LM567V is as follows (top view):

• Pin 1: Output Filter Capacitor (C₀)
• Pin 2: Loop Filter Capacitor (C_LF)
• Pin 3: Input Signal (V_IN)
• Pin 4: Ground (GND)
• Pin 5: Timing Resistor (R_T)
• Pin 6: Timing Capacitor (C_T)
• Pin 7: VCO Output (VCO Out)
• Pin 8: Output Transistor (Open Collector)

Design Considerations

When designing with the LM567V, the following guidelines should be observed to ensure optimal performance:

• Center Frequency Selection: The center frequency (f₀) is determined by the external timing resistor (R_T) and capacitor (C_T). Use the formula: f₀ ≈ 1 / (1.1 × R_T × C_T).
• Bandwidth Adjustment: The detection bandwidth is set by the capacitor at Pin 2 (C_LF). A larger capacitor results in a narrower bandwidth.
• Input Signal Conditioning: Ensure the input signal is within the recommended amplitude range (10 mV to 3 V RMS) and free from excessive noise or distortion.
• Power Supply Decoupling: Use a 0.1 µF ceramic capacitor close to the V_CC pin to minimize noise and ensure stable operation.
• Output Load Considerations: The open-collector output requires an external pull-up resistor when driving logic circuits. Select a resistor value based on the desired sink current and voltage levels.

Conclusion

The LM567V is a versatile and reliable tone decoder IC suitable for a wide range of frequency detection applications. Its adjustable center frequency, programmable bandwidth, and logic-compatible output make it an excellent choice for designers working in telecommunications, remote control, and industrial automation. By following the recommended design practices and selecting appropriate external components, the LM567V can deliver robust performance in diverse operating conditions.