Pressure sensors are disclosed that may perform health monitoring in-situ in harsh operating environments. The pressure sensors may be based on a Clapp-type oscillator that includes one or more resistors, one or more inductors, capacitors, a sensor, and a transistor. Such pressure sensors may be particularly well-suited various applications, such as gas turbine engines, oil and gas extraction, vehicle engines, and exhaust monitoring.

Variable frequency oscillators allowing wide tuning range and low phase noise is disclosed. In an illustrative embodiment, a first transistor has a first terminal (e.g. collector) connected to a reference voltage, and a second terminal (e.g. emitter) connected to a first terminal of a first current source and to ground. The first transistor further has a third terminal connected to a first inductor and to a first capacitor connected to the emitter of the first transistor and also to a second capacitor connected to ground. A second transistor is similarly constructed. In order to achieve a variable frequency oscillation between the emitters of the two transistors, a variable tank capacitor is connected between the inductors, forming a circuit connecting in series all passive components composing the LC tank, masking most of parasitic capacitances.

A variable frequency oscillator comprising a first transistor (10) and a second transistor (20); wherein the first transistor (10) has a first terminalcollectorwhich is connected to a reference voltage, and a second terminalemitterwhich is connected to a first terminal of a first current source (13), which second terminal is connected to ground, and a third terminalbaseconnected to a first terminal of a first inductor (14) and to a top terminal of a first capacitor (11), wherein the first capacitor (11) has a bottom terminal which is connected to the second terminalemitterof the first transistor (10) but also to a top terminal of a second capacitor (12) having a bottom terminal being connected to ground; wherein the second transistor (20) has a first terminalcollectorwhich is connected to a reference voltage, and a second terminalemitterwhich is connected to a first terminal of a second current source (23), which second terminal is connected to ground, and a third terminalbaseconnected to a first terminal of a second inductor (14) and to a top terminal of a third capacitor (21), wherein the third capacitor (21) has a bottom terminal which is connected to the second terminalemitterof the second transistor (20) and also to a top terminal of a fourth capacitor (22) having a bottom terminal connected to ground; wherein the first and second inductors (14, 24) have a second terminal which are connected via a circuit (100) achieving variable capacitance, so as to form a circuit connecting in series all passive components composing the LC tank, so as to achieve a variable capacitance which can be used for performing a tuning of the oscillator, and wherein the second capacitor (12) and the fourth capacitor (22) are both connected to the physical ground thereby avoiding a 2nd harmonic common mode oscillation that might dominate over the differential fundamental one and might destroy the first and the second transistors (10, 20).