Abstract: A signal processor such as an ADPCM decoder (128b) receives an input signal. As part of the CCITT Recommendation G.726 algorithm, an inverse adaptive quantizer (41) processes the input signal to provide a quantized difference signal d.sub.q (k). When enabled, a noise detector (50) samples signal d.sub.q (k) once for each of a predetermined number of received samples. The noise detector (50) adds the absolute value of signal d.sub.q (k) to a total energy estimate. At the end of the predetermined number of samples, the noise detector (50) compares the total energy estimate to a product of a noise threshold and the predetermined number. If the total energy estimate exceeds this product, then a noise indication is provided. In another embodiment (228b) a noise detector (250) compares an existing energy estimate signal d.sub.ml (k) computed by an adaptation speed control block (48) as part of the G.726 algorithm to an energy threshold to save processing time.

Abstract: A bandgap voltage reference circuit (50, 100) which operates at low power supply voltages provides a reference current as either a one- or a two-.DELTA.V.sub.BE voltage across a first resistor (82, 133). A current proportional to the reference current is mirrored into one terminal of a second resistor (94, 133) to provide the bandgap voltage. Compensation for base currents injected into the circuit (50, 100) by two transistors forming the .DELTA.V.sub.BE reference is provided. In one embodiment (50), base currents of first (66) and second (87) transistors which have equal emitter areas and collector current density as the two transistors (68, 85) forming the .DELTA.V.sub.BE reference compensate for the injected base currents. In another embodiment (100), a single transistor (127) injects current substantially equal to the sum of the base currents of the two transistors (116, 121) forming the .DELTA.V.sub.BE reference.

Abstract: A low voltage precision current generator includes an amplifier, a first transistor, a current portion, and an output portion. The amplifier has first and second input terminals and changes an output voltage until voltages at the first and second input terminals are equal. An input voltage which may be a stable reference voltage or a variable voltage is received at the first input terminal. The second input terminal is connected to the current portion in order to provide a reference current proportional to a voltage difference between the voltage at the second input terminal and a power supply voltage. The amplifier controls the conductivity of the first transistor in order to regulate the voltage at its second input terminal. A precision current precision current proportional to the reference current is then provided.

Abstract: A bandgap reference circuit providing a continuous output reference voltage. The bandgap reference circuit comprises an operational amplifier, an output circuit, and a compensation circuit. The operational amplifier receives a first input signal and a second input signal and provides an output signal in response to a difference in voltage between the first input signal and the second input signal. The output circuit receives the output of the operational amplifier and provides an output reference voltage. The output circuit provides the first input signal and the second input signal to the operational amplifier in such a way as to maintain the output reference voltage at a substantially constant value. The compensation circuit provides a current to the output circuit to compensate for currents conducted from the bases of transistors in an input stage of the operational amplifier, thereby making the output reference voltage more stable.

Abstract: An analog two pole filter is provided which uses a single amplifier to implement a predetermined transfer function. The filter has a differential input and converts the two inputs to a single output utilizing the same amplifier which performs the filtering function. By coupling a capacitor across the differential input and utilizing the differential aspect of the input signals, the capacitor may be implemented with half the capacitance otherwise required to implement the predetermined transfer function, thereby minimizing circuit area.