Optimized Ultralow-Power Amplifier for OOK Transmitter With Shaped Voltage Drive

For a highly efficient ON-OFF keying (OOK) transmitter, a microwatt-level ultralow-power (ULP) driver and power amplifier (PA) are designed. For efficient amplification with very high optimum impedance in the ULP application, a class-C topology is implemented and loadpull simulations are carried out to show that the proposed PA can achieve good efficiency at high optimum load impedance without any harmonic tuning. In addition, a voltage-shaping driver is optimized together with the PA for an efficient drive. The proposed driver shapes the PA input voltage into a waveform having a small conduction angle. The shaped input voltage drives the PA to a saturated operation for good efficiency even if the supply voltage is low in the drive stage. The developed driver and PA are implemented in a CMOS 65-nm process and support a 1-Mb/s OOK modulated signal. The implemented PA achieves a drain efficiency of 50.8% at the -6.8-dBm output power and 49.8% at the -10-dBm output power when transmitting continuous 1 signal.