Abstract
The traditional calibration method often needs the factory test. Each device under test (DUT) has to pass through complicated test procedure, and costs time and resources. Several automatic calibration techniques have been developed to solve this problem. But present calibration methods usually need extra circuits, and these circuits mostly require analog approach, which increase the device cost. The Voltage Controlled Oscillator (VCO) is an essential component in frequency synthesizers (FS). Fabricated by deep submicron processes, the VCOs exhibit characteristics that are highly dependent on the process variations, such as resistor, capacitor and transistor threshold voltages. For this reason, calibration systems and techniques for frequency synthesizers are needed to provide a precise setting of the VCO’s operating curve. Based on the proposed method, the calibrating signals are generated for adjusting its center frequency and gain during power up or when responding to an initiation signal. The proposed automatic calibration circuit uses digital approach to determine the final operating curves. This is done by selecting the switches associated with the coarse tuning apparatus until an appropriate curve is obtained. The proposed technique has been successfully demonstrated in a prototype system, which shows fast and accurate auto-trimming operation.