A system and method for tuning a transistor-based circuit. The system includes a negative impedance converter circuit having a capacitor, a first transistor, and a second transistor. As a current travels through the capacitor, the first transistor and the second transistor each sample voltage at the capacitor and invert the voltage at an input of the negative impedance converter circuit. The negative impedance converter circuit also has a third transistor in series with the capacitor. The third transistor has a base voltage. Changing the base voltage of the third transistor changes the voltage sampled by the first transistor and the second transistor.

An active filter reduces Electro-Magnetic Interference (EMI) created by current flowing through a power line. The active filter connects to the power line at a single node through a connection capacitor. A sense current flows through the connection capacitor when the power line current changes. This sense current is applied to a gain control circuit having cross-coupled PNP transistors that drive currents to both terminals of a variable capacitor. The variable capacitor converts these currents to a voltage that is injected back into the power line through the connection capacitor as an injected compensation voltage that compensates for the sensed current.

An active filter reduces Electro-Magnetic Interference (EMI) created by current flowing through a power line. The active filter connects to the power line at a single node through a connection capacitor. A sense current flows through the connection capacitor when the power line current changes. This sense current is applied to a gain control circuit having cross-coupled PNP transistors that drive currents to both terminals of a variable capacitor. The variable capacitor converts these currents to a voltage that is injected back into the power line through the connection capacitor as an injected compensation voltage that compensates for the sensed current.

Packaged integrated circuit devices include an oscillator circuit having a resonator (e.g., quartz crystal, MEMs, etc.) associated therewith, which is configured to generate a periodic reference signal. A built-in self-test (BIST) circuit is provided, which is selectively electrically coupled to first and second terminals of the resonator during an operation by the BIST circuit to test at least one performance characteristic of the resonator, such as at least one failure mode. These test operations may occur during a built-in self-test time interval when the oscillator circuit is at least partially disabled. In this manner, built-in self-test circuitry may be utilized to provide an efficient means of testing a resonating element/structure using circuitry that is integrated within an oscillator chip and within a wafer-level chip-scale package (WLCSP) containing the resonator.

An amplifier circuit according to the present invention includes a first block, a second block, a transformer, and a reference node and operates as a negative impedance converter circuit. A circuit configuration formed by a first transistor and at least one first passive component in the first block with respect to a first terminal of the transformer and a circuit configuration formed by a second transistor and at least one second passive component in the second block with respect to a second terminal of the transformer are the same as each other.

An amplifier circuit according to the present invention includes a first block, a second block, a transformer, and a reference node and operates as a negative impedance converter circuit. A circuit configuration formed by a first transistor and at least one first passive component in the first block with respect to a first terminal of the transformer and a circuit configuration formed by a second transistor and at least one second passive component in the second block with respect to a second terminal of the transformer are the same as each other.

A compensation circuit reduces the negative effects of antenna-to-antenna coupling between proximately located antennas. The compensation circuit is coupled between first and second antenna ports. A first transmit/receive path extends from radio frequency (RF) circuitry to the first antenna port. A second transmit/receive path extends from the RF circuitry to the second antenna port. Antennas are coupled to each of the antenna ports. The compensation circuit includes negatively coupled first and second inductors, which are coupled in series between the first antenna port and the second antenna port. At least one shunt acoustic resonator is coupled between a fixed voltage node and a common node between the first and second inductors. In operation, the compensation circuit presents a negative capacitance between the first antenna port and the second antenna port over the first frequency range to reduce the effects of the antenna-antenna coupling.

An active filter reduces Electro-Magnetic Interference (EMI) created by current flowing through a power line. The active filter connects to the power line at a single node through a connection capacitor. A sense current flows through the connection capacitor when the power line current changes. This sense current is applied to a gain control circuit having cross-coupled PNP transistors that drive currents to both terminals of a variable capacitor. The variable capacitor converts these currents to a voltage that is injected back into the power line through the connection capacitor as an injected compensation voltage that compensates for the sensed current.

An active filter reduces Electro-Magnetic Interference (EMI) created by current flowing through a power line. The active filter connects to the power line at a single node through a connection capacitor. A sense current flows through the connection capacitor when the power line current changes. This sense current is applied to a gain control circuit having cross-coupled PNP transistors that drive currents to both terminals of a variable capacitor. The variable capacitor converts these currents to a voltage that is injected back into the power line through the connection capacitor as an injected compensation voltage that compensates for the sensed current.

A signal processing circuit includes a signal receiving circuit for generating a first input signal and a second input signal; a signal output circuit for generating a first output signal and a second output signal according to the first input signal and the second input signal; a negative impedance circuit, for amplifying the first input signal at the first input terminal to generate a first amplified input signal at the second output terminal, and for amplifying the second input signal at the second input terminal to generate a second amplified input signal at the first output terminal; a first capacitor; a second capacitor; wherein the first capacitor and the second capacitor have different DC voltage levels at both terminals, such that the impedance-signal variation rate of the negative impedance circuit is lower than a predetermined level.