Bridge circuits
Bridge circuits are among the most elemental and powerful electrical tools. They are found in measurement, switching, oscillator, and transducer circuits. Additionally, bridge techniques are broadband, serving from DC to bandwidths well into the GHz range. Being the electrical analog of the mechanical beam balance, they are also the progenitor of all electrical differential techniques. An almost uncountable number of tricks and techniques have been applied to enhance linearity, sensitivity, and stability of the basic configuration. In particular, transducer manufacturers are quite adept at adapting the bridge to their needs. Careful matching of the transducer's mechanical characteristics to the bridge's electrical response can provide a trimmed, calibrated output. Similarly, circuit designers have altered performance by adding active elements to the bridge, excitation source, or both. A primary concern is the accurate determination of the differential output voltage. Bridge amplifiers are designed to accurately extract the bridge's differential output from its common mode level. The common mode suppression circuits shown require a negative power supply. Often, such circuits must function in systems where only a positive rail is available. The bridge's inherent nonlinear output is also accommodated by the processor. Level transducers which measure angle from ideal level are employed in road construction, machine tools, inertial navigation systems, and other applications requiring a gravity reference.