A tunable transimpedance amplifier (TIA) is presented in this letter. By incorporating a mechanism for gain and bandwidth tuning, the TIA can be adjusted to achieve optimum circuit performance with a lowest bit-error-rate (BER) for high-speed applications. The proposed circuit is implemented in a 0.18-mum CMOS process. Consuming a dc power of 34mW from a 2.0-V supply voltage, the fabricated TIA exhibits a variable -3-dB bandwidth from 3.9 to 7.6GHz while maintaining a transimpedance gain of 52dBOmega. With a 7.5-Gb/s 231-1 pseudo-random bit sequence, the measured input sensitivity of the TIA is -19 dBm at a BER of 10-12