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Method and circuit for implementing an impedance, in particular for DC telephonic applications
No full textThe invention relates to a method and circuit for implementing an impedance associated with a monolithically integrated telephone subscriber circuit connected to a telephone line having a pair of terminals. The circuit consists of a resistor connected serially to one terminal of the telephone line, and a series of current mirror circuits. The current mirror circuits are connected in a closed loop configuration to the one terminal of the telephone line. The current mirror circuits divide, by a predetermined factor, the value of the resistor when a DC or very low frequency signal is input to the telephone circuit
Supply circuit device for a user's telephone circuit, having a low voltage loss
No full textA circuit is described which comprises an operational amplifier, two resistors connected between the telephone line and the inputs of the amplifier, a capacitor which is charged via a first bipolar transistor controlled by the amplifier via a first FET transistor, a second bipolar transistor in parallel to the connection of the first transistor and the capacitor, a second FET transistor, identical to the first and having its source and gate terminals connected to the corresponding terminals of the first, and two current generators connected to the drain terminals respectively of the first and the second FET transistor and to the bases, respectively, of the first and second bipolar transistor. The currents of the two generators and the other parameters of the circuit are such as to hold the first and second bipolar transistors in a conductive and a switched off state respectively, except when the line voltage fails below a minimum predetermined value; in which case the first and second transistors commute to the switched off and conductive states respectively. The circuit has a lower "voltage loss" than known circuits
AC integrated coupler with phase equalizer
No full textA monolithically integrated AC coupling circuit is presented for DC uncoupling and AC coupling (typically in telephone applications) to an input signal. The AC coupler includes a high-pass filter having a first pole at a frequency well below a frequency of interest and a zero at zero frequency. The AC coupler also includes a pole/zero doublet between the frequency of the first pole and the frequency of interest. The frequency of the first pole for a specified error is increased by addition of the doublet. Because the frequency of the first pole is increased, the size of the required capacitors is decreased, enabling integration. An implementation of the circuit using switched capacitor techniques is described. An alternative circuit employing a unit gain interface is presented. The alternative circuit reduces the dynamic range and driving voltage requirements of its field-effect transistors
Splitting of a supply current drawn from a telecommunication system's line among a plurality of user's circuits
No full textA circuit is provided in telecommunication terminal equipment for splitting a limited supply of current received from a subscriber's line current among a plurality of functional circuits according to their priority rank. The circuit uses a differential pair of current delivering transistors and a special circuit to monitor the actual current of absorption of at least the functional circuit of highest rank to produce a control signal that is used for modifying the drive conditions of the current delivering transistors. All current exceeding the actual absorption needs of the highest rank functional circuit is distributed to the other functional circuits and the prior art practice of sinking unneeded current through a dissipative shunt voltage regulator associated with each functional circuit is avoided. This same principle may be advantageously applied also to functional circuits of progressively lesser rank of priorit
High ratio current mirror with enhanced power supply rejection ratio
No full textThe PSRR (power supply rejection ratio) of a current mirror circuit is increased by cascoding the output transistor of the current mirror, and the precision of the circuit is enhanced by employing a frequency compensated gain stage utilizing a field effect transistor to drive a bipolar current output transistor
1.5-V high-performance SC filters in BiCMOS technology
No full textThe authors describe two low-voltage switched-capacitor (SC) filters: one can operate from a minimum supply of 1.5 V and the other from a minimum supply of 2 V (for typical parameter values). Both filters use a fully differential architecture and are fabricated in a standard BiCMOS technology. The lowest supply filter, operated from a 2-V supply, has an SNR (signal-to-noise ratio) of 92 dB and a THD (total harmonic distortion) of -70 dB for a 2.4-Vpp differential signal. Power consumption and area per pole are 60 μW and 0.18 mm2, respectively, with a clock frequency of 447 kHz. The realized filters can be used as building blocks to implement more complex functions, like the active synthesis of a given impedance in line-fed telecom system
RC filter for low and very low frequency applications
No full textAn RC filter for low or very low frequency applications, comprising a resistor between the filter input and output, and an amplifier connected after the resistor and having an output fed back to the amplifier input through a capacitor. This simple design allows the known Miller Effect to be utilized to produce a filter having a high time constant while employing small-size components which occupy little space in integrated circuits
Driver circuit compatible with low supply voltages
No full textA driver circuit, for an electronic switch which is to be operated from a clock signal, comprises an inverter driven by the clock signal, and a voltage doubler which is connected to supply the inverter and connected to be driven by the complementary clock signal
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