Northern Telecom Limited

Nortel Networks Corporation

Petre Popescu

Mark Stephen Wight

Paul Thomas Banens

Kathryn Louise Howlett

The invention relates to a driver circuitry suitable for controlling an operation of a laser or an optical modulator and providing extended dynamic range of the output power and enhanced quality of the output signal. It comprises a power control unit, a pre-driver stage and an output stage. The pre-driver stage and the output stage include differential amplifiers, the output stage amplifier preferably having a cascode configuration. The pre-driver stage provides a preliminary amplification of an input signal which is received and further amplified by the output stage. The power control unit operates in response to a reference signal, e.g. variable DC voltage or a feedback signal, and generates two control signals which control operating points of the pre-driver and the output stage in such a manner that higher output power of the driver corresponds to the higher output signal from the pre-driver stage. Conveniently, both the pre-driver stage and the output stage may be controlled by the same control signal. Depending on the product requirements, the driver circuit can be monolithically integrated with a device to be driven by the circuit.

High speed variable output power driver

A gain control amplifier includes an input differential circuit having a pair of transistors, the emitters of which are coupled via a pair of emitter resistors. The input differential circuit includes a current sink for providing an operating current. With variation of the operating current, the gain control amplifier's gain is varied. Two emitter coupled differential amplifiers are connected to the input differential circuit having a current sink. A current flowing in the transistors of the emitter coupled differential amplifier and the input differential circuit is split by an additional emitter coupled differential circuit having a current sink. A current splitting factor is controlled in response to the voltage difference between the collectors of the two transistors of the two emitter coupled differential amplifiers. Since the relatively small currents flow in the emitter resistors, noise caused thereby is relatively low. Thus, it provides a wide input dynamic range with low noise. The gain control amplifier is used in a variable gain amplifier and an automatic gain control amplifier.

Gain control, variable gain and automatic gain control amplifiers including differential circuit transistors and current splitter

An RC circuit with voltage controlled delay is provided. The circuit comprises a matched pair of RC delay elements, driven by outputs of a pair of amplifiers comprising a fixed gain amplifier and a variable gain amplifier having gain m so that the delay is dependent on a gain control voltage. Preferably, the circuit is operable in a regime wherein the gain m is linearly dependent on an input control voltage so that the circuit delay is also linearly dependent on the input control voltage. Advantageously, where the amplifier gain has non-linear dependence on a gain control voltage, a control voltage generator comprising a linear to logarithmic converter is used to provide an effective linear operation in response to an input control voltage. The circuit is preferably operated in differential mode, with RC circuit elements implemented simply as resistors and capacitors, and the amplifier and active elements provided by bipolar transistors. Alternatively, MOS devices may be used for R, C elements and active devices. Although differential operation is preferred, single ended operation is an option if one of the pair of input signals is a reference voltage.

RC circuit

In methods and apparatus for controlling a phase relationship of two signals, a supplementary phase adjustment signal is generated. The supplementary phase adjustment signal has a zero value when an actual phase relationship of the two signals deviates from a desired phase relationship by less than a threshold phase deviation, and has a non-zero value when the actual phase relationship deviates from the desired phase relationship by more than the threshold phase deviation. The phase relationship of the two signals is adjusted in response to a sum of the supplementary phase adjustment signal and a phase adjustment signal which is proportional to the deviation of the actual phase relationship from the desired phase relationship. The methods and apparatus are particularly applicable to alignment of clock signals with data signals.

Phase alignment methods and apparatus

A circuit for generating a pair of quadrature output signals from a pair of quadrature input signals in which the frequency of the output signals is double that of the input. The circuit consists of two dual phase shifters, two symmetrical multipliers and a phase controller. The circuit is fabricated by conventional integrated circuit processing technology. A method of generating frequency doubled quadrature output signals is disclosed.

Quadrature signals frequency doubler

A differential ECL (emitter coupled logic) circuit, with differential inputs and output and no series gates, comprises a plurality of transistor pairs. The differential ECL circuit can operate at high speed as there are no series gates and its noise margin is large because of differential operation. The differential circuit can be implemented into various logic circuits such as XOR (exclusive OR)/NXOR, OR/NOR, AND/NAND.

Differential ECL circuit

A family of second order active filters is described. A general form of the filter comprises an input terminal, an output terminal, and a common terminal, a first reactance and a resistance coupled in series between the input and common terminals, a first emplifier coupled from a connection point between the first reactance and the resistance to the output terminal, a first potential divider between the input terminal and one of the output and common terminals, a second amplifier coupled from a tapping point of the first potential divider via a second reactance to the connection point, a second potential divider between the output terminal and the common terminal, and a third amplifier coupled from a tapping point of the second potential divider via a third reactance to the connection point, at least one of the reactances being inductive and at least one other being capactive. Different configurations are described for low-pass, notch, high-pass, band-pass, and all-pass filters, in some of which the first potential divider and second amplifier and second reactance, or the second potential divider and third amplifier and third reactance, are omitted.

Second order active filters

A second order active filter comprises an input terminal, an output terminal, and a common terminal, a capacitive T-network comprising three capacitors and, in parallel therewith, a resistive T-network comprising three resistors, the terminals of the T-networks being connected respectively via a first amplifier to the output terminal, via a buffer to the input terminal, and to the common terminal, a potential divider between the output and common terminals, and a second amplifier having an input coupled to a tapping point of the potential divider and an output coupled via a resistor to the central junction of the capacitive T-network and via a capacitor to the central junction of the resistive T-network. In different configurations of the filter, the component coupled to the common terminal may be omitted from one of the T-networks, or from both of the networks with another potential divider coupled between the input and common terminals and a third amplifier coupling its tapping point to one of the networks.

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Kanata, Canada

Petre Popescu