LM567 Tone Decoder IC Features, Datasheet and Applications

In this post I have explained the main specifications, datasheet and working principle of the IC LM567, which is a precise phase-locked loop with synchronous AM lock detection and power output device.

In simpler terms the IC LM567 IC is a tone decoder chip which is designed basically for recognizing a specified frequency band, and activating the output in response to the detection.

Needless to say this chip can be used for a number of different applications, the most common being in the field of remote controls, and security systems.

Block Diagram

Absolute Maximum Rating

Absolute maximum rating refers to the values indicating the maximum tolerable capacity of the IC in terms of voltage, current, and power dissipation. The following table explains the absolute maximum rating of the IC LM567 for the relevant parameters:

Pinout Working and Specifications

Referring to the the above shown IC LM 567 internal configuration diagram, the pinout function of the IC may be understood from the following points:

Pin#4 and Pin#7 are the positive (Vdd) and the negative (Vss) supply inputs respectively for the IC.

Pin#3 is the sensing input of the input, which is used for detecting a given phase-locked loop frequency, in other words this pin will lock-on with the matching center frequency which may be set inside the IC through a pair of external RC network.

The Pin#5 and 6 are used for creating the center frequency by setting up the values of R1, C1 as required, and this frequency is used by the sensing input pin#3 to lock-in and create a logic zero at pin#8 which is the output pin of the IC.

Output Pin#8 is normally logic high and becomes logic zero as soon as a matching frequency is detected at pin#3 of the IC.

Pin#1 and pin#2 are used for ensuring proper filtration of the involved frequencies so that the IC does not create any false output due to any existing spurious or stray noise interferences.

Main Features of LM567:

Extensive settable frequency range (0.01 Hz to 500 kHz), meaning the sensing passband may be set right from 0.1 to 500 kHz, giving an option of a huge range so that unlimited unique configuration can be achieved from this chip.

Highly stable of center frequency, which assures precise passband limits making the unit very reliable with the detection functions.

Independently controllable bandwidth (up to 14%), as the feature suggests, the bandwidth is also adjustable to a reasonable degree.

High out-band signal, and noise rejection, which again assures high reliability during the detection and implementation of the said functions.

Logic-compatible output with 100 mA current sinking capability, which allows the output to handle relatively higher loads without employing an additional buffer stage such as a transistor driver stage.
Inherent immunity to false signals, which ensures that the chip never produces false results due to incorrect frequency detection or in the presence of stray or spurious instantaneous signals.

Frequency adjustment over a 20-to-1 range with an external resistor, this feature again makes the chip highly flexible and dynamic.

The three important Parameters Associated with the IC LM567 may be understood with the following points:

Phase locked loop center frequency

It’s the free running frequency of the in-built current controlled oscillator circuitry in the
absence of an input signal.

Detection Bandwidth

This is the frequency range which may be provided to the above center frequency, within which the presence of an input signal having a threshold voltage of above 20mV  causes the output of the IC to become low. This feature refers to the loop capture range.

Lock Range

It is the maximum range of frequency which would enable the output to switch to logic zero in the presence of a relevant input signal having a threshold voltage above 20mV.

Detection Band

It is the magnitude which indicates the level of optimal detection, focused around the center frequency. It’s given by the formula:

Detection Band = (fmax + fmin – 2fo)/2fo,

where fmax and fmin are the frequencies thresholds of the detection band, fo is the center frequency.

Application Hints

The IC567 may be considered as a versatile chip because it provides an unlimited range of applications in the field of electronics, some of them are discussed below:

1. Touch-Tone decoding: The human touch response may produce different frequencies when employed with this chip, it can be suitably decoded by using many IC LM567 configurations.
2. Carrier current remote controls: Our existing mains wiring can be very effectively used as a medium of transfer for communicating between the rooms or for controlling appliances remotely from one room to the other. The actions can be implemented by using a LM567 IC.
3. Infrared controls (remote TV, etc.): Since the center frequency of LM567 is tightly locked, it may be used for detecting IR waves precisely from the given handset. Unlike ordinary IR remote controls, this circuit is better immune to stray RF or IR disturbances created from switching AC mains appliances.
4. Frequency monitoring and control: Again since the LM567 IC has an inbuilt precise frequency detection range, which can be used for monitoring a given range of frequency accurately.
5. Wireless intercom: Just like Carrier current remote controls, the IC LM567 may also be suitably  implemented in wireless intercom systems.
6. Precision oscillator: The phase locked loop feature in the proposed IC also facilitates its application as a precision oscillator for achieving precisely adjusted oscillations or frequencies.

Summarizing More Information About LM567 IC

The LM567 circuit is an active filter most commonly used as a frequency decoder. The LM567 circuit detects and responds to a specific frequency that can be set and adjusted in advance. It is an IC with a wide range of diverse applications, particularly in the field of remote control.

General information:

• Its nominal working power supply potential is 5V DC. It consumes approximately 7 mA.
• It is an extremely complex integrated circuit, consisting of no fewer than 62 transistors!
• With the help of a minimal number of peripheral components, its usage is very straightforward.
• In particular, by using an adjustable RC component, it is possible to vary the detection range in a ratio of 1 to 20.
• Its output can accept a current compatible with TTL technology (up to several tens of mA).
• The bandwidth is adjustable from 0 to 14%.
• Naturally, the circuit is equipped with an effective noise rejection and immunity device against noise and parasitic signals.
• It is characterized by a high stability of the frequency setting value. The frequency itself can be adjusted within very wide proportions, ranging from 0.01 Hz to 500 kHz.

The IC is represented in the form of a rectangular package with 8 pins, arranged in two rows of 4.

The positive power supply is connected to pin 4, while the negative (ground) connection is made to pin 7.

The input signal is applied to pin 3, and the output is available at pin 8.

Pins 1 and 2 are connected to capacitors that are linked to the negative power supply.

The first capacitor filters the output signal, while the second capacitor determines the bandwidth width.

Finally, pins 5 and 6 are connected to a capacitor and a typically adjustable resistor, respectively. These components determine the detection frequency parameters.

Application Circuit

Referring to the example circuit shown below, the signal applied to pin 3 can take the form of a sinusoidal waveform or a square waveform, symmetric or asymmetric.

However, the manufacturer recommends an RMS (root mean square) value ranging from 50 to 200 mV.

For a sinusoidal signal, the RMS value is determined by the relationship: Veff = 0.35 x Vpp (where Vpp is the peak-to-peak value).

If the signal is a square waveform, the RMS value is calculated using the relationship: Veff = Vpp / 2 (where Vpp is the potential difference between the high and low levels).

If the signal includes a DC component, which is often the case, it needs to be blocked by using a coupling capacitor at Pin 3.

Pin 6 should be connected to ground through a capacitor, denoted as C1.

Pins 5 and 6 are connected by a resistance, variable or fixed, denoted as R1.

The detection frequency is then determined by the relationship: FO = 1 / (1.1 x R1 x C1) (where R1 is in ohms and C1 is in farads).

The internal circuitry employs the principle of phase lock loop.

By using a capacitor, denoted as C2, connected between pin 2 and ground, the bandwidth width can be determined as a percentage relative to F0:

Bandwidth (%) = 1070 (√Veff / FO x C2) (where Veff is in volts, FO is in hertz, and C2 is in picofarads).

The capacitor C3, which connects pin 1 to ground, plays a role in determining the number of input signal cycles needed for detection confirmation.

By selecting a value for C3 that is close to the value of C2, this number of cycles varies inversely with the width of the bandwidth.

For example, if the bandwidth width decreases from 10% to 0%, the required number of cycles for triggering the detection will increase from 30 to 300.

This feature provides an additional means of ensuring that only desired signals are detected while minimizing false detections.

Furthermore, when FO (the target frequency) is detected, the output at pin 8, which is normally held high by a resistor (ranging from 10k to 100k) connected to the positive supply, rapidly switches to a low state, providing a clear indication of the detection.