Abstract: A semiconductor current follower and method using a copy of the input current from a current mirror to insure that the input impedance remains a virtual ground for both unidirectional and bidirectional signals.

Abstract: An electronic filter for passing predetermined frequencies includes resistive and capacitive components that need not be rated to handle the input voltage. An input signal is converted to a second signal that is proportional to the logarithm of the input signal (and therefore of much smaller magnitude than the input signal), and then low, high, bandpass filtered with an RC filter. The filtered signal is reconverted to an output signal that is proportional to the inverse logarithm of the filtered signal. The filter may be embedded in a current mirror that may be used in telephone system subscriber line interface circuit.

Abstract: A circuit and method for isolating a subscriber line interface circuit ("SLIC") from the ringer generator in a telephone system. The circuit uses a gain blocking device to provide a signal gain when the ringer generator is not being utilized and to provide a high impedance when a ringer signal is present. The high impedance may be provided through an amplifier circuit which is tri-stated when the amplifier is not energized.

Abstract: A ground key detector for a subscriber line interface circuit (SLIC) uses information from the tip and ring voltage sensing resistor RS1 and RS2 to determine whether the ring side of the telephone line has been grounded, as when a ground key or fault occurs. The voltage difference between a tip voltage and ground is converted to a DC tip current, and the voltage difference between a ring voltage and a battery voltage is converted to a DC ring current, and the DC ring current is compared to a combination of the DC tip current and a reference current to determine whether the ring side of the telephone system has been grounded. The DC tip and ring currents may also be used to determine whether a fault exists in the tip side of the telephone line, and in the hybrid circuitry of the SLIC.

Abstract: A current mode subscriber line interface circuit (SLIC) for telephone system in which AC and De impedances for tip and ring connections of the SLIC are separately set. A DC filter separates the DC and AC components of tip and ring currents, and a current amplifier amplifies the AC components separately from the DC components. A pair of resistors set the AC impedance value, and also may be used to set SLIC four-wire to two-wire gain separately from SLIC two-wire to four-wire gain.

Abstract: The analog to digital converter 300 has voltage reference circuitry 326 which includes a bandgap generator and a correction circuit 5300. The bandgap generator includes first and second NPN transistors 5211-5224, 5231-5232 of differing emitter areas and an operational amplifier 5202 with inputs sensing the collector current of the first and second NPN transistors 5211-5224, 5231-5232. First and second NPN transistors 5211-5224, 5231-5232 have their bases tied together. The output of the amplifier 5202 drives the bases of the NPN transistors 5211-5224, 5231-5232 through a resistor divider 5251-5253.

Abstract: A two-step analog-to-digital converter and BiCMOS fabrication method. The fabrication method provides pseudosubstrate isolation of digital CMOS devices from the analog devices. The converter uses NPN current switching in a flash analog-to-digital converter and in a digital-to-analog converter for low noise operation. CMOS digital error correction and BiCMOS output drivers provide high packing density plus large output load handling. Timing control aggregates switching events and puts them into intervals when noise sensitive operations are inactive. The fabrication method uses a thin epitaxial layer with limited thermal processing to provide NPN and PNP devices with large breakdown and Early voltages. Laser trimmed resistors provide small long term drift due to dopant stabilization in underlying BPSG and low hydrogen nitride passivation.

Abstract: A voltage follower input stage having a correction or bootstrap circuit to effectively remove the parasitic capacitance by bootstrapping the capacitance so that both sides of the parasitic capacitance follows voltage level changes.

Abstract: A correction circuit is provided to improve current accuracy by sensing the error current of a first variable current source and substracting it from the output of a second variable current source. It also increases output impedence by sensing incremental output current and cancelling its effect.

Abstract: A current source including a correction circuit configured as a secondary current source for adding current to the output as a function of base current of a primary transistor current source and increase impedance level of the output terminal by adding incremental current to the output terminal equal to the incremental current of the primary transistor current source to cancel the effect of the primary transistor current source on output impedance. The improved current source also improves the performance of a current mirror or pulley and a differential to single-ended current converter.

Abstract: The front end of an operational amplifier having an improved slew rate and high gain current output capabilities. The amplifier includes a slew enhancement or large signal stage connected in parallel to a normal front end or small signal stage. The small signal stage supplies a transconductance output which is approximately linearly related to the input until its slew rate limit. The slew enhancement stage is designed to provide slew current when the small signal stage reaches a selected threshold such as its slew rate limit, thereby providing an increased output current response to an increasing differential input voltage beyond the slew rate of the small signal stage. The large signal stage can be optimized to provide a greater input linear dynamic range, faster slew rate and improved efficiency.

Abstract: The front end of an operational amplifier having an improved slew rate and high gain current output capabilities. The amplifier includes a slew enhancement or large signal stage connected in parallel to a normal front end or small signal stage. The small signal stage supplies a transconductance output which is approximately linearly related to the input until its slew rate limit. The slew enhancement stage is designed to provide slew current when the small signal stage reaches its slew rate limit, thereby providing an increased output current response to an increasing differential input voltage beyond the slew rate of the small signal stage.

Abstract: An operational amplifier having an input stage, a voltage gain stage, a current gain or buffer stage and a feedback connected between the output of the buffer stage for supplying to the voltage gain stage a current which varies in proportion to the voltage gain stage output to increase the output impedance of the voltage gain stage.