Abstract
In this thesis, a digital-to-frequency converter (DFC) designed for 2.4 GHz ISM-band applications is proposed. The DFC directly produces an analog periodic output signal which frequency is proportional to the input digital code. Since there is no feedback control loop, the converter can achieve very fast frequency-switching which is important for some wireless applications, for example: high data-rate FSK transmitters. The proposed design consists of a digitally controlled oscillator (DCO), a high speed gated ripple counter, and a digital control circuit for capacitance and frequency calibration. The DCO-based design provides stable and precise output frequency by avoiding noisy analog control. The digital-to-frequency conversion is realized by transfer the input frequency code to the capacitor control code of the DCO. Considering hardware complexity and process variations, two transfer algorithms for piecewise linear approximation and non-binary-weighted switched-capacitor arrays are proposed to minimize output frequency error. This design is implemented in TSMC 0.18 µm 1P6M CMOS process and the chip area is 1 x 1 mm2. According to the measurement results, the oscillation frequency is 2.34 ~ 2.59 GHz with 255 MHz tuning range, and the phase noise is less than -102 dBc/Hz at 500 kHz offset. The effective frequency resolution is 7 bits and the total power consumption is 13 mW under 1.8 V supply voltage.