TABLE OF CONTENTS One of the most challenging blocks to design in data links is the pre-amplifiers, arising from the stringent requirement on both noise and bandwidth. Pre-amplifiers are often implemented using trans-impedance configurations to take the advantages of their relatively low noise and large bandwidth. As compared with low-impedance and high-impedance configurations [145], the high current gain of transimpedance pre-amplifiers is achieved from an intermediate voltage amplification stage [146, 147]. Due to the existence of high-impedance nodes, the drawbacks of voltagemode circuits can not be avoided. In addition, this configuration requires a current-to-voltage conversion stage, usually a passive resistor. The thermal noise of the resistor deteriorates the noise performance. It is advantageous to amplify the current directly to avoid the use of lumped resistors and take the advantages of current-mode approaches [148].
The large capacitance of the channels through which data are transmitted, together with the input impedance of pre-amplifiers, often set the bandwidth of data links [31]. Pre-amplifiers with a low input impedance is critical. A low input impedance of current-mirror pre-amplifiers is achieved traditionally by increasing the width of the input transistor and its dc biasing current, however, at the expense of a large chip area, a high level of power consumption, and reduced bandwidth. The techniques that are based on local active feedback at the input have been proposed recently to reduce the input impedance of current-mode circuits [35, 33, 36]. As demonstrated quantitatively in [27] that the effectiveness of these techniques diminishes at high frequencies.
