This article describes the design and implementation of a compact CMOS RC frequency reference based on N-type diffusion (N-diff) resistors and metal-insulator-metal (MIM) capacitors. It consists of a frequency-locked loop (FLL) that locks the period of a voltage-controlled oscillator (VCO) to the time it takes a current source to charge a capacitor to a reference voltage. Conventionally, the temperature compensation of such FLLs involves the use of resistors with different temperature dependencies. In this work, however, this is done by using two bipolar junction transistor (BJT)-based current sources with different temperature dependencies to charge a MIM capacitor and generate a reference voltage across an N-diff resistor, respectively. Implemented in a standard 180-nm technology, the resulting frequency reference achieves small size (0.028 mm²), moderate inaccuracy (±900 ppm) from -40 ^°C to 125 ^°C, and low drift (±1600 ppm) after accelerated aging. The versatility of the proposed temperature compensation scheme is validated by replacing the N-diff resistor with a P-poly resistor. However, the latter exhibits greater inaccuracy (+2000/-2500 ppm) and more drift (-2600/-8100 ppm) after accelerated aging.

A 400-MHz/2.4-GHz combo transceiver (TRX) integrated chip (IC) Supporting simultaneous dual-band communication is designed and fabricated in a 65-nm CMOS technology for compact wireless personal area network applications. The IC is composed of a 3-10 Mb/s quadrature phase shift keying (QPSK)/offset QPSK (OQPSK) TRX working at the 400-500 MHz band, and a 1-3 Mb/s Gaussian frequency shift keying (GFSK)/half sine OQPSK (HS-OQPSK) TRX at the 2.4-2.4835 GHz band for the Bluetooth low energy/IEEE 802.15.4 protocols. The presented combo TRX IC requires one single antenna without any bidirectional RF coupler, to support simultaneous dual-band communication. Two key circuit techniques, namely, the combination biasing technique to suppress the high-order harmonics and the active in-band interference cancellation, are adopted to tackle the crosstalk interference between the two bands during simultaneous dual-band operation. Measurement results show that the in-band interference presented to the 2.4-GHz receiver due to the 400-MHz transmitter is suppressed by 19 dB with the presented design techniques.