Abstract: A switched capacitance circuit, using a switched operational amplifier structure as an input switch of the switched capacitance, is provided with a new biasing circuit. An additional switched capacitor, switched alternately to power supply and to ground, is connected to the output side of the primary switched capacitor. Precision is retained while ensuring a rail-to-rail dynamic range, without requiring boosted control phases. Special arrangements may be implemented for controlling the amplitude of switching spikes when so required. A fully differential embodiment is also feasible with additional advantages.

Abstract: The speech circuit matches the impedance of the telephone line by synthesizing a complex impedance using a positive feedback loop which has a single resistor (11), and cancels out the side tone using a subtractor (20') which extracts from the signal (Va) coming from the line a signal (Vb) correlated to the signal to be transmitted. In order to achieve cancellation of the side tone unaffected by the noise produced in the impedance synthesizing circuits, the signal (Vb) is derived by processing the signal present in the resistor (11) at the output of the feedback loop.

Abstract: A low-voltage transconductor circuit in which the common mode gain of a first transconductor stage is compensated by a second transconductor stage (connected in parallel with the first transconductor stage) which has no differential mode transconductance, and which is connected so that its common mode transconductance offsets the common mode transconductance of the stage. This greatly reduces the common mode current signal at the output, while avoiding the necessity for a current sink at the source of the input transistors.

Abstract: A controlled gain transconductor (20) which comprises a transconductance stage (3) having at least two input terminals (I1, I2) and at least two output terminals (O1, O2), an active load (4) connected to the output terminals of the transconductance stage and a control circuit (5) for the active load (4) connected between said output terminals (O1, O2) and the active load (4).Also provided is a circuit portion (10) being a replica of the transconductance stage (3), the active load (4) and the control circuit (5). This replicated portion (10) has an output connected to the control circuit (5) of the transconductor (20) to provide a predetermined voltage value (Vc) required for adjusting the DC gain of the device.

Abstract: A 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.

Abstract: An analog multiplier circuit includes three transconductance stages. One of the transconductance stages, receiving a first differential voltage, conducts a differential current responsive to the first differential voltage from the other two transconductance stages. The differential current changes the transconductance in the other two transconductance stages, which are cross-coupled with one another. The second differential input voltage is presented to the other two transconductance stages in parallel, resulting in an output differential current or voltage based on the product of the first and second differential input voltages. Each of the transconductance stages is implemented in BiCMOS, and each includes two differential legs, each having a MOS transistor receiving an input signal and a cascode bipolar transistor.

Abstract: The invention relates to a transconductor circuit with a double input and a single output, comprising two input transistors (M1, M2) whose primary conduction terminals (D1, S1, D2, S2) are respectively connected together; in this way, variations in load current and voltage can be made lower, thereby also lowering distortion from changes in their transconductance.

Abstract: A 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.

Abstract: The 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.

Abstract: A 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 priority.

Abstract: A threshold voltage generator for a field-effect transistor, being of a type adapted to compensate for variations of the threshold voltage from a nominal value, comprising a first amplifier having a first input connected to a current generator; a second amplifier connected ahead of a second input of the first amplifier and having an input connected to another current generator; and a third amplifier connected after the first amplifier and having an output adapted to produce the value of said threshold voltage.

Abstract: The 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.

Abstract: A circuit for synthesizing an impedance associated with a telephone subscriber's circuit connected to a two-wire telephone line is described. The circuit of the invention is adapted to synthesize a complex impedance which can function both as a termination impedance and a balance impedance. The termination impedance utilizes a positive feedback loop structure having a loop gain which is at all times less than unity. The circuit that implements both the termination and balance impedances with sidetone suppression is also described. Each of the embodiments is realizable with a single external component consisting of a resistor.

Abstract: An 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.

Abstract: A transconductor stage for high-frequency filters of a type which comprises an input circuit portion having signal inputs and an output circuit portion, incorporates a pair of field-effect transistors having respective gate and source terminals in common, and has the output portion formed of a pair of bipolar transistors connected to the aforesaid field-effect transistors.

Abstract: A 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.

Abstract: A transconductor differential stage for high-frequency filters, which has a MOS differential input pair with common sources. The drain of each MOS input is connected to the emitter of an npn bipolar. These two matched bipolars have their gates connected together with the gate of a third bipolar, which is diode-connected. Two matched current sources feed the two bipolars, and a third current source feeds the third bipolar. A single controlled current sink is connected to the sources of both MOS input transistors, and also (through a resistor) to the third bipolar.

Abstract: A circuit arrangement for enhancing the transconductance of a differential amplifier stage comprising a pair of MOS transistors, having respective source electrodes connected together through a circuit node, comprises a pair of active components respectively connected in each of the connections between the aforesaid electrodes and the aforesaid node and serving a characteristic function corresponding to that of a negative value resistor. This arrangement enables the transconductance of the differential stage to be increased while keeping the dissipated electric power low and the area occupied in an integrated circuit small.

Abstract: A circuit arrangement for increasing the gain-bandwidth product of a CMOS amplifier having a differential cell input stage comprises, within said input stage:a pair of active components having a characteristic function which corresponds with that of a negative value resistor, for increasing the transconductance of the stage,a pair of capacitors being each respectively associated with a corresponding one of the active components to introduce a pole/zero pair in the frequency response from the amplifier, andan additional input stage cross-connected to the differential cell for bringing the frequency value of the zero a predetermined distance away from the amplifier clipping frequency.

Abstract: The source is apt to generate a fully-differential reference voltage at the output terminals, whereto precisely-balanced loads are applied. The voltage reference is obtained from a bandgap voltage source fed with currents proportional to the temperature, in order to minimize thermal voltage variations. Suitable circuits for starting the normal source operation after switching on are also provided.