A Tuning Technique for Bandwidth of Programmable Gain Filter

We propose a common-mode variable voltage (CMW) method to improve the bandwidth of low pass filter for ultra-wideband (UWB) transmitter. It is based on leap-frog structure to design a 250 MHz 8^th -order GM-C Chebyshev low pass filter. In the analytic results, tuning the common-mode reference voltage (VCM) of common-mode feedback circuits of transconductor, the cutoff frequency of filter can be calibrated to overcome the process variation and temperature dependencies. This approach can effectively reduce the chip size and do not need excess circuits. The filter combines a resistor network and 4times13 decoder to program the gain of filter and is implemented in a CMOS 0.18 mum process and power dissipation is 18 mW under 1.8 V power supply. Measurement results show that the filter can be reformed 50% bandwidth and the gain can be programmed from -14 dB to -38 dB with 2 dB step. The attenuation at 285 MHz and 330 MHz is 16 dB and 32 dB, respectively, and the total harmonic distortion (THD) of programmable gain filter is -37 dBc for 1Vpp differential input signal at 150 MHz.