Lucent Technologies Inc.

Csr Technology Inc.

Michael D Womac

Paul C Davis

Kirk B Ashby

Malcolm Harold Smith

The voltage-controlled current source receives a control voltage from an operational amplifier which itself receives a reference voltage at one input from a bias circuit. The voltage-controlled current source applies current to the base of the amplifier's main transistor. The base of the transistor is also coupled to the input node of the amplifier through a DC-blocking capacitor and through a feedback loop to the other input of the operational amplifier. The voltage-controlled current source operates to maintain the voltage at the base of the transistor relatively constant for a wide range of input signal levels. As a result, the amplifier is able to operate at relatively low power supply voltages (e.g., as low as 2V) without suffering from premature gain compression at relatively high input signal levels (e.g., as high as 0.4V).

Integrated amplifier having a voltage-controlled current source

In low-voltage circuits, there is often insufficient voltage to use a current source to bias a transconductance amplifier stage. This is particularly true in mixers where a switching circuit must be stacked on top of the transconductance input stage. One way around this problem is to get 'double-duty' out of the input differential pair, using it both for gain stage and for DC bias. This is done by AC coupling in a high-frequency input signal, while using a low-frequency, DC-coupled circuit to establish the proper bias level. One common technique is to use a simple current mirror scheme to establish the DC level. Proper biasing using this technique requires good matching of resistance. In some implementations of transconductance amplifiers, particularly those that use inductors as degeneration elements, series resistance of the inductor and interconnect resistance can cause significant errors in the bias current. This invention addresses that problem by using an operational amplifier with a current-sensing resistor and a low-frequency feedback loop to compensate automatically for any resistance errors. The operational amplifier drives the feedback voltage (generated in accordance with the sensed voltage at the current-sensing resistor and applied to one input of the operational amplifier) towards a reference voltage that is applied to the other input of the operational amplifier to bias the transistor(s) in the transconductance amplifier for desired operating conditions.

Growing community of inventors

Blandon, PA, United States of America

Michael D Womac