A 900MHz RF(radio frequency) receiver system composed of low noise amplifier(LNA), oscillator, and frequency down conversion part has been designed with specific emphasis on low power consumption. To adopt Zero_IF scheme to reduce the power consumption as well as filters. The important system specifications such as frequency offset in oscillator, bandwidth of low pass active filter and channel spacing are extensively studied. We proposed for the first time that the oscillator power level can be increased by lowering Q-value of the LC tank circuit. The required harmornic suppression is obtained by interstage matching. Adopting above two techniques, we succeeded to increase the oscillator power by 2dB at same bias current with comparable harmornic suppression. The dimension of our experimental RF system shows very small size, i.e., 4mm height and 30mm x 30mm area, with -115dBm input sensitivity and 4.6mA current consumption at 2V operation, which is comparable to the currently used RF system for pager which adapted the double conversion IF scheme. This RF system is suitable for very small size and low power 900MHz pager system.
