Method and apparatus using feedback to correct the production of magnitude and phase relationships between two sinusoidal signals for use in a ratio-transformer capacitance bridge

A method of driving ratio transformers, which generate voltage ratios, in a ratio transformer capacitance bridge, comprising

• supplying a digital signal to a digital-to-analog converter,
• converting the digital signal to an analog signal,
• delivering the analog signal to the ratio transformer
• monitoring the signals from the ratio transformer using an analog-to-digital converter, and
• using a digital representation of the ratio transformer output to correct the supplied digital signal.

A driving circuit for a ratio transformer capacitance bridge, comprising

• a DSP for generating digital signals representing frequency and amplitude of a driving signal for a ratio transformer,
• a digital-to-analog converter for converting the digital signals to an analog signal of a frequency and amplitude representative of the digital signal,
• a monitor for the DSP comprising an analog-to-digital converter, and
• connection of the digital representation of the ratio transformer output back to the DSP.

A method of developing precision analog signals using a DSP, comprising

• using the DSP to develop a digital signal,
• converting the digital signals to two analog signals using respective digital-to-analog converters,
• periodically sampling the two analog signals and supplying to the DSP the results of such sampling for error correction,
• said periodic sampling comprising sampling each of said analog signals by respective analog-to-digital converters and alternating the analog-to-digital converters to which respective analog signals are delivered.

A ratio transformer capacitance bridge for measuring the value of a capacitance, comprising

• a bridge circuit,
• one or more ratio transformers coupled in the bridge circuit,
• a detector coupled across the bridge to detect the extent of balance or imbalance,
• a reference capacitance,
• a DSP and digital-to-analog converter circuitry to drive the respective ratio transformers with respective signals having a prescribed relation,
• a monitor circuit monitoring the outputs of the ratio transformers, and providing feedback to the DSP to maintain the prescribed phase and/or amplitude relation.