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How to Simplify the Design of an RF Remote Control

 post:2016-11-22


  Designing radio frequency (RF) remote controls has never been easier thanks to the advent of highlyintegrated, single-chip RF solutions. System-on-chip (SoC) transmitter solutions greatly simplify the process of designing a remote control and reduce system bill of materials (BOM) cost by eliminating the need for numerous discrete components. 

Remote controls come in many different sizes, shapes and wireless technologies and are widely used in the consumer market as accessories for a wide range of products, such as televisions, video games, stereo systems, lighting controls and home automation including garage door/gate openers, air conditioning units, fans and automobiles with remote keyless entry (RKE) key fobs. 

The most common remote controls use infrared (IR) technology because of the relatively low cost of IR components, but these IR-based controls suffer from many drawbacks including requiring line-of-sight pointing, limited operating angles, short transmission range, reflection problems and high current consumption associated with the IR LEDs, which leads to low battery life. RF remote controls resolve these issues and are appearing in greater numbers because consumers are demanding a much better user experience. In addition, technology improvements are closing the RF-IR price gap.

All RF remote controls share common features as shown in the simplified block diagram in Figure 1. The basic components of an RF remote control are buttons for the user to input a command, a microcontroller unit (MCU) to process the user commands into digital messages, an RF transmitter (RF TX) to modulate and transmit the message, an antenna, and a battery to provide power to the remote control. 

The common challenges manufacturers face in designing RF remote controls are to provide consistent maximum transmission range, ensure long battery life and maintain low system costs. Maximizing transmission range involves transmitting as much power as possible (within governmental regulatory limits) while providing a receiver with excellent sensitivity since the total transmit distance is a function of both the transmitter output power and the sensitivity of the receiver. 

From the remote control side, the design goal is to set the RF output power to the government limit, which implies that all remote controls should have the same output performance, since they all transmit within the same limits. This would be true in an ideal world, but, in the real world with real components and manufacturing tolerances, it is practically impossible to transmit at this optimum power every time with every remote control manufactured on the production line. Moreover, interference from a user’s hand holding the remote control or even touching a button (known as the “hand effect”) changes the impedance of the antenna and thus changes the transmit output power. 

This real-world effect can reduce the effective radiated power (ERP) of a remote control and easily result in output power 6 dB below the government limit, with a corresponding 2x reduction in transmit distance per Friis’s free space path loss equation. 

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Keywords:design remote control,rf remote control,simplify remote control
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