Tag Archive for: antenna impedance

The Si4010 transmitter, the latest member of Silicon Labs’ EZRadio® line of wireless products, is the industry’s first single-chip remote control IC, requiring only one external bypass capacitor, a printed circuit board (PCB), battery and an external casing with push buttons to form a complete remote control. The Si4010 includes a patented antenna tuning circuit that automatically fine-tunes the antenna for optimum transmit power on every button press. With standard remote control designs, variations in the RF transmitter, component and antenna manufacturing tolerances and the environment can lead to large antenna inefficiencies and wasted power.

An additional feedback loop is incorporated into the power amplifier (PA) to maintain constant output power by monitoring the voltage at the output of the PA and adjusting the PA’s current drive to compensate for changes in the antenna impedance. This feedback loop works to maintain constant output power in spite of temperature variations and the “hand effect,” which, as stated above, changes the antenna impedance when a person’s hand is covering the remote control. The net result of antenna tuning is to provide consistently reliable and optimal performance on every button press while reducing the cost and design complexity of the RF matching requirements. Remote controls designed with the Si4010’s automatic antenna tuning feature can reliably and consistently operate at the government transmit limit for maximum transmit range.

Battery life is an important consideration for any portable electronic device, especially a remote control. When we consider typical remote control usage, more than 99 percent of the time, a remote control is waiting for a user to activate a button press. During this time, the Si4010 consumes less than 10 nA at room temperature, making it an ideal choice for battery-powered applications. Additionally, wake-on-touch GPIOs further minimize current consumption of the remote control and extend battery life.

One of the most important considerations in any remote control design is minimizing total system design cost, which is influenced by many factors besides component costs, including labor, inventory, test, and manufacturing yield. By far, the dominant low-cost RF remote control solution on the market today uses an MCU and a surface acoustic wave (SAW)-based RF transmitter.

The wide acceptance of this design topology stems primarily from its low cost and simplicity. A SAW device is resonated with transistor Q1 in a Colpitts oscillator structure to form the carrier frequency, and transistor Q2 provides the output power amplification and isolation needed for stable operation. Data from the MCU is applied directly to the SAW resonator to form the OOK modulated signal, and GPIO6 from the MCU supplies the voltage (VCC) to the SAW-based transmitter. This entire solution uses 24 external components, including the MCU, one bypass capacitor, a quartz crystal used to clock the MCU, and a PCB with a trace antenna and capacitor. It has an RF component cost (excluding the PCB, MCU and bypass capacitor) of .77 USD in 100,000-unit volumes. The .77 RF BOM cost does not include the cost of the MCU, bypass capacitor or PCB. Traditionally, this has been the lowest component cost solution available for reliable RF transmission. From a system cost perspective, the large BOM count increases other costs, such as labor, inventory and tests, and reduces manufacturing yield.