2.5GHz PLL with current matching charge-pump for 10Gbps transmitter design

In this paper, we describe a mixed PLL architecture for low jitter clock generation that use a proposed charge pump and output buffer. The newly designed charge-pump circuit is composed of two differential inputs, the signals of UP and DN from the PFD, and an op-amp that matches between the upper current and the lower current. If the two currents are matched in charge-pump there is a low ripple voltage, which is VCO control voltage. The new charge pump circuit has a good immunity from MOSFET width and length variation. Also, we build the differential current driving output buffer for high speed signal processing on a chip. In the newly designed output buffer circuits, the push-pull source follower is added to the previous differential current driving output buffer. As the result, the jitter characteristic has been improved. The PLL with current matching charge-pump has been designed by 0.18μm one-poly four metal CMOS technology and simulated by HSPICE. From the simulation results, it is shown that the VCO control voltage is at least 0.6mV.