Nec Electronics Corporation

Macronix International

Young-Jen Sun

Yeong-Sheng Lee

A portion of a differential charge pump circuit is partially replicated and is utilized as a replica circuit to define the common-mode voltage VCM of the differential output voltages of the charge pump circuit that drives a voltage controlled oscillator (VCO) in a PLL system application, or a voltage-controlled delay (VCD) circuit in a DLL system application. The replica circuit includes a high gain operational amplifier and at least three MOS transistors electrically coupled to the differential charge pump circuit. The operational amplifier generates the DC output voltage VO which is used to define the common-mode voltage VCM of the charge pump circuit. The three transistors are configured in replica of one-half of the charge pump circuit. The operational amplifier is provided with a bias voltage at the inverting-end input terminal. During operation, the high gain of the operational amplifier forces the non-inverting end of the operational amplifier to the same value as the bias voltage supplied to the inverting-end input. This voltage equalization effect is referred to as the replica effect. As a result of the replica effect, the charge pump's DC output voltages OUTP and OUTN follow the voltage at non-inverting end of the operational amplifier which results in stable operation of the differential charge pump and a control circuit which is suitable for high-frequency (greater than 400 MHz) application of phase-locked loop (PLL) and delay-locked loop (DLL) systems applications.

High speed differential charge pump apparatus and method using a replica

A current switch for high-speed and high-resolution digital to analog converters (DACs) employs MOSFET devices to control the current switch output in response to binary input signals at logic level voltages. The current switch reduces ringing of the output current that occurs when switching takes place to improve DAC high speed performance by protecting current steering MOSFET transistors against application of the full swing voltage of the binary input signal by applying lower voltage switching signals in place of the full swing logic level voltages. Furthermore, the current switch compensates for parasitic capacitances within the current steering MOSFET transistor that drives the output current.

Growing community of inventors

Fremont, CA, United States of America

Young-Jen Sun