Lucent Technologies Inc.

Kirk B Ashby

Paul C Davis

Michael D Womac

Malcolm Harold Smith

Iconomos A Koullias

Brian K Horton

There is disclosed a transconductance amplifier receives a voltage input and provides a current output. The transconductance amplifier includes a current mirror having a lowpass filter between transistors implementing the current mirror.

Transconductance amplifier with wideband noise filtering

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

A multi-stage mixer circuit has two or more mixer stages, each stage having a mixer core and successive mixer cores being separated by one or more current mirrors. By using current mirrors to process the currents generated by the mixer cores, instead of current-to-voltage and voltage-to-current converters as in the prior art, the present invention provides a mixer circuit with reduced signal distortion and power dissipation. In one embodiment, the two mixer cores of a two-stage mixer circuit are implemented using the same type of transistor devices (e.g., N-type), and there are two current mirrors between the mixer cores. In another embodiment, the two mixer cores of a two-stage mixer circuit are implemented using different types of transistor devices (i.e., one N-type and the other P-type), and there is only one current mirror between the mixer cores. A mixer circuit of the present invention may have an initial voltage-to-current converter to convert an input voltage signal into a current for the first mixer core. A mixer circuit of the present invention may also have a current-to-voltage converter to convert the current generated by the last mixer core into an output voltage signal. Alternatively, the last mixer core could be followed by a final current mirror that mirrors the current generated by the last mixer core.

Mixer with current mirror load

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.

Bias circuit for transconductance amplifier

A variable gain amplifier (VGA) may be useful in applications where the input amplitude is constant but the output must vary over a wide range. Some VGAs have a desirable exponential control characteristic, but an undesirable temperature characteristic that causes the gain to change with temperature when the control voltage is held constant with respect to temperature. The present invention is directed to a circuit that will convert a control signal (e.g., a voltage) that is constant with temperature into a voltage that can be applied to a VGA in such a way that the temperature variation of the VGA is eliminated without changing the desirable exponential control characteristics.

Temperature compensation for variable gain amplifiers

A compensation scheme for differential- or single-input transconductance amplifiers relies on an active feedback path with a resistive pole-splitting compensation circuit. The resistive compensation circuit causes pole-splitting of the two dominant poles, moving one pole to a slightly lower frequency and the other to a much higher frequency compared to the dominant poles of the uncompensated amplifier. A DC-blocking capacitor may also be placed in series with the resistor of the compensation circuit to allow for proper biasing of the circuit. By selecting appropriate values for the passive elements in the compensation circuit, the compensation scheme of the present invention can cause the amplifier to operate in a stable, linear manner over the same or even a larger bandwidth than an equivalent amplifier without compensation. The present invention does not suffer the problems of standard narrowbanding compensation schemes associated with high frequency cut-off.

Broadband linear transconductance amplifier with resistive

A method of and apparatus for effecting single sideband modulation which mixes and sums the quadrature and in-phase components of a baseband signal with the in-phase and quadrature components of an intermediate frequency (IF) signal to form in-phase and quadrature components of a sum signal having a frequency equal to the sum of the frequencies of the baseband and intermediate frequency signals and which mixes and sums the quadrature and in-phase components of an RF carrier signal with the in-phase and quadrature components of the sum signal to form a single-sideband signal.

Single sideband double quadrature modulator

An inductive structure is provided which displays an increased self-inductance and improved Q at high frequencies. The improvement resides in the disposition proximate the inductive structure an amount of magnetic material to increase mutual inductance between adjacent portions of the inductor's conductive path with current flow.

Growing community of inventors

Reading, PA, United States of America

Kirk B Ashby