摘要:
A technique for reducing phase shift of a signal passing through a large thin film resistor on an insulating layer includes applying a signal to one terminal of the thin film resistor and also to one end of an underlying doped epitaxial region. The opposite terminal of the thin film resistor is connected to a virtual ground or virtual reference voltage produced by an inverting input of an operational amplifier. The corresponding opposite end of the epitaxial layer is connected to ground or other reference voltage. The voltage gradients produced by currents flowing through both the thin film resistor and the epitaxial layer are equal, so that substantially no incremental charging current flows through capacitance between the thin film resistor and the epitaxial layer. Phase shift of the signal flowing through the thin film resistor is thereby avoided.
摘要:
An isolation amplifier includes a voltage-to-duty-cycle modulator, a non-galvanic isolation barrier, and a demodulator converting a duty-cycle-modulated signal transmitted across the isolation barrier to an analog voltage replica of the analog input voltage. The modulator circuit includes a first current switching means which produces a first current that is switched between positive and negative values in response to an output from a comparator that can be referenced to a noise-synchronized signal. The first current is summed with an input current and the difference is integrated and input to the comparator, the output of which produces the duty-cycle-modulated signal. The demodulator includes a second current switching circuit for producing a second current that is switched between positive and negative levels in response to the duty-cycle-modulated signal received across the isolation barrier and includes circuitry for algebraically summing the input current with the second current and integrating the result to produce the analog output voltage. The modulator circuit and demodulator circuits are fabricated on a single semiconductor area to produce the close matching between components of the first and second current switching circuits. The area is cut in half to produce two chips, which are connected to two isolation barrier capacitors. In the demodulator, a sample and hold circuit synchronized with the duty-cycle-modulated signal transmitted across the isolation barrier samples the output of the integrator.
摘要:
A two-terminal temperature-compensated current source includes a first transistor having its emitter connected to a first terminal, its base connected to the base of a second transistor, and its collector coupled to a current mirror. The second transistor has its emitter coupled to the first terminal by a first resistor and its collector coupled to the current mirror. A second resistor is coupled between the first terminal and the base of the first transistor. The current mirror is coupled between a second terminal and the collectors of the first and second transistors so that all current supplied to the current mirror from the second terminal flows into the collectors of the first and second transistors. A third transistor has its base coupled to the collector of the first transistor, its emitter coupled to the base of the first transistor, and its collector coupled to the second terminal. The current in the first resistor has a positive temperature coefficient, and the current in the second resistor has a negative temperature coefficient. The temperature coefficient of the total current flowing between the first and second terminals is adjusted by adjusting the ratio between the first and second resistors.