Infrared receiving head (also known as infrared receiving module, IRM) is an IC module that integrates the infrared receiving PD light -sensitive diodes, zooming, filtering and comparator output, structural shielding, etc. Due to the integrated internal integrated circuit, the application of infrared receiving heads in infrared products is used to simplify the design of the circuit.
A commonly used shape of infrared receiving head has three pins, namely the power supply VDD, power supply (GND), and data output (OUT). The pins of the receiving head are different due to the different models, and the differences of pins due to the different appearance of the receiving head.
1/infrared receiving head is commonly encapsulated as follows:
Common packaging forms of infrared receiving heads are as above:
2/Infrared receiving internal equivalent circuit is as follows:
The function of the chip contains: digital mold hybrid circuit: from the benchmark source, front amplifier, I/V conversion circuit, automatic gain control (AGC) amplifier, limited amplifier, band filter, comparative circuit, gain control circuit, integral circuit circuit, integral circuit circuit Composition with waveform plastic surgery circuit
Internal function description:
Photo Diode: The remote control receiver signal and convert it to a current signal. (NA ~ tens of UA)
I-V: Convert the current signal output by Photo Diode to an easy-to-process voltage signal. (MV)
AMPLIFIER: For the convenience of signal processing, the voltage signal is processed. (Dozens of MV ~ Hundreds of MVs)
AGC Control: According to the size of the signal and noise, the amplitude of the gain is adjusted. When there is no signal, the noise signal output is prevented.
B. P. F: Select the signal with the corresponding frequency of the carrier signal to pass through, and filter out the unnecessary noise signal.
WaveForm Detector: Through comparators, the carrier component is detected, and then the original signal is restored by comparison processing.
Waveform RECTIFER: The waveform detected by the detection of the detection circuit through the Schmidt trigger.
OUTPUT Stage: Built -in top -pull resistance, with low power consumption output characteristics. When there is no signal, receiving head standby consumption is small, which can improve the trust of the product.
The overall workflow is as follows: I/V conversion module converts the optical current detected by the infrared optoelectronics diode to a voltage signal. This signal is enlarged by the front amplifier, variable -increasing amplifier, and limited amplifier amplifier. The noise outside, then remove the carrier by the comparator and integralizer, and the demodolic waveform is restored to the transmitted signal emitted by the transmitted end after plastic surgery.
The explanation of the automatic gain function is as follows:
1. When the input signal is small or no signal, the VGA control signal is reduced, and the gain of VGA becomes larger;
2. When the signal detects the signal, the VAG control signal increases, and the gain of VGA becomes smaller;
3. When the signal suddenly disappears, the VGA control letter starts to decline after maintaining a certain period of time, and VGA also maintains the original gain after a certain period of time.
The external factors that affect the function of the infrared receiving header are as follows:
1. The transmitting device has different transmission power, causing changes in the input signal of the receiving end;
2. The distance between the launch device and the infrared receiving device is different, and the signal strength received is also different;
3. The atmosphere between the launch device and the infrared receiving device is strong and weak in absorption of infrared light signals
4. Various background light sources, such as sunlight, lighting, etc., will also interfere with the light signal to be transmitted. When a noise signal, the remote control distance will be shortened, or no signal will occur.
5 Electromagnetic interference can be used to receive electromagnetic shielding bodies through infrared heads to block or reduce electromagnetic transmission, which is one of the important means to inhibit electromagnetic interference. The shielded shell has two purposes. One is that the electromagnetic can be leaked out of the internal area with the internal radiation of the limit, and the other is to prevent external radiation interference from entering a certain area. When the electromagnetic field is isolated by metal materials, the intensity of the electromagnetic field will be significantly reduced. This phenomenon is the shielding effect of metal materials. If the receiving head works in an environment with strong electromagnetic interference, it can be shielded by installing an iron shell.
The typical application of the receiving head is as follows:
At the front end of IRM’s VCC and GND input signals, design a blocking filter (R-C Decoupling Filter with Lower Cut-Off Frequency). Generally, using R = 100Ω, C = 47㎌, you can confirm the noise The periodic of the periodicity of FC = 1/2πRC can be designed. The R1 and C1 parameter range is generally: 33 Euros 0.1 micro method.