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An integrated, single-chip ASK (Amplitude Shift Keyed) RF transmitter designed specifically to meet the needs of low-cost loop antenna transmitters is now available from Micrel Semiconductor. The MICRF102 QwikRadio™ transmitter complements Micrel's existing family of QwikRadio™ single-chip receivers.

Highly integrated in SOIC-8 packaging, the MICRF102 requires only five external components. It incorporates transmit power control and unique automatic antenna tuning.

Automatic tuning of the antenna eliminates the need for manual tuning in production, making it much easier to manufacture and more reliable than previous solutions. The power control function ensures consistent output power across varying operating conditions and over the lifetime of a battery. Included within the power control function is the ability to set the transmit power by controlling the voltage on a power control pin.

Loop antenna transmitters are popular in many low-cost and space-limited applications, but come with manufacturing problems. Previously, the high-Q inherent in a loop antenna, combined with manufacturing tolerances of the antenna itself, required manufacturers to manually tune the transmitter antenna in production. Those who chose not to tune had to accept significant differences in transmitted power from device to device.

Even a correctly tuned device has problems; a user's hand in proximity to the antenna modifies the resonant properties of the antenna circuit and detunes it. The MICRF102 overcomes both of these problems by continually tuning itself to the antenna; if the resonant properties change, the MICRF102 automatically adapts.

The MICRF102 operates off a 5 V supply, consumes 7.5 mA (mark) and 4 mA (space) supply current and has a shutdown pin to further conserve power. It is provided in a SOIC-8 package.

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