Patent Application
20090243729
Transimpedance amplifiers (TIA) are widely used in the receiver side of fiber optical transceiver modules. In such transceiver modules, the positivie-instrinsic-negative (PIN) photo detector detects the optical light signal strength and converts the optical signal into an electrical current input signal. An amplifier in a negative feedback arrangement converts the current input signal into a voltage to provide transimpedance amplification. Sometimes several stages of amplifiers are utilized to provide final output voltage. When the input signal is too strong, the generated current signal may be too large which pushes the voltage at the output node to be too low, thereby causing the amplifier go into saturation. As a result, the transimpedance amplifier may not operate properly anymore, and the signal could be distorted. Such a situation is referred to as overload.
Claimed subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. However, such subject matter may be understood by reference to the following detailed description when read with the accompanying drawings in which:
It will be appreciated that for simplicity and/or clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, if considered appropriate, reference numerals have been repeated among the figures to indicate corresponding and/or analogous elements.
In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components and/or circuits have not been described in detail.
In the following description and/or claims, the terms coupled and/or connected, along with their derivatives, may be used. In particular embodiments, connected may be used to indicate that two or more elements are in direct physical and/or electrical contact with each other. Coupled may mean that two or more elements are in direct physical and/or electrical contact. However, coupled may also mean that two or more elements may not be in direct contact with each other, but yet may still cooperate and/or interact with each other. For example, “coupled” may mean that two or more elements do not contact each other but are indirectly joined together via another element or intermediate elements. Finally, the terms “on,” “overlying,” and “over” may be used in the following description and claims. “On,” “overlying,” and “over” may be used to indicate that two or more elements are in direct physical contact with each other. However, “over” may also mean that two or more elements are not in direct contact with each other. For example, “over” may mean that one element is above another element but not contact each other and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean “one”, it may mean “some, but not all”, it may mean “neither”, and/or it may mean “both”, although the scope of claimed subject matter is not limited in this respect. In the following description and/or claims, the terms “comprise” and “include,” along with their derivatives, may be used and are intended as synonyms for each other.
Referring now to
In one or more embodiments, transceiver 100 may be capable of receiving an optical signal from an optical transmission medium 122 such as an optical fiber or the like, and may comprise on a receive side thereof an optical-to-electrical (O/E) converter 110 which may comprise, for example, a photodetector or the like; a transimpedance amplifier (TIA) 112; a limiting amplifier (LA) 114; and a clock data recovery module 116. Clock data recovery module 116 may include a clock data and recovery (CDR) circuit 118 coupled to a decoder 120 to provide an electrical output 124 representative of the optical signal received from transmission medium 122. On a transmit side, transceiver 100 may comprise a laser 126; a laser driver circuit 128; and retimer circuit and/or encoder 130. Retimer circuit 130 receives a signal in electrical form from input 132 and provides these signals to laser driver 128 which provides current variations proportional to the received signal with which laser 126 is driven. Laser 126 then generates optical signals proportional to the received current levels for transmission over an optical transmission medium 134 which may comprise, for example, an optical fiber or the like. Transceiver 100 as shown in
In one or more embodiments, the receive side of transceiver 100 receives optical information signals propagating along transmission medium 122 and outputs an electrical equivalent via output 124. The optical information signals are incident on O/E converter 110 where optical energy is converted to an electrical current proportional to the received optical signals. The expression “information signals,” as used herein, refers to a signal which has been coded with information. These signals are amplified during propagation by optical amplifiers disposed along the transmission medium 122 and are incident on O/E 130 which may be arranged to detect an individual wavelength and/or a range of optical wavelengths. The electrical signals generated by the photodetector of O/E converter 110 may be relatively weak so they may be converted to a voltage equivalent, as well as being squaring-off as digital pulses, regenerating clock signals, and/or noise filtering induced by transmission and dark noise generated by the photodetector of O/E converter 110. The current signal generated by photodetector of O/E converter 110 may be converted into a corresponding voltage for further processing. This conversion may accomplished by TIA 112 which typically may be characterized by a higher transimpedance on the front end and a lower impedance on the back end. TIA 112 provides higher transimpedance with lower noise amplification. Because the current signal received by TIA 112 from the photodetector of O/E converter 110 may be relatively small, TIA 112 may also function as a preamplifier to provide an output signal having an amplitude ranging from about a few millivolts to a about a few hundred millivolts. In optical communications systems, the average power of the received optical signals may vary by orders of magnitude depending on span losses, fiber nonlinearities, and so on. Thus, TIA 112 may be arranged to operate over a wider dynamic range of input currents received from the photodetector of O/E 112.
Limiting amplifier (LA) 114 may functions to produce a consistent waveform in response to an input received from TIA 114. Because the input signal received by LA 114 from TIA 110 may still be relatively small, LA 114 may provide a relatively higher gain factor to generate higher output signal levels. Such gain typically may be provided via multiple amplification stages in order to achieve higher stability at higher bandwidths than would otherwise be achieved with a single higher gain amplification stage. In other words, LA 114 is capable of increasing the voltage gain of the signals received from TIA 112 to a signal level suitable for CDR circuit 118. CDR circuit 118 is capable of recovering both the data and/or the clock signal embedded in the input data stream received by the photodetector of O/E converter 110. The input and output waveforms received and generated by transimpedance amplifier 112 are shown in and described with respect to
Referring now
Referring now to
In one or more embodiments, when the signal across feedback resistor Rf is sufficiently high and thus the gain of the feedback loop of amplifier 312 is sufficiently high, a control signal is provided by control circuit 314 via transistor Q3 to cause transistor Q3 to leak away all, or nearly all, of the DC component of the input current Iin, and the DC voltage level at node “in” and node “out1” will be equal, or nearly equal. The resulting output voltage waveform at node “out1” controlled by control circuit 314 is shown in and described with respect to
Referring now
Although the claimed subject matter has been described with a certain degree of particularity, it should be recognized that elements thereof may be altered by persons skilled in the art without departing from the spirit and/or scope of claimed subject matter. It is believed that the subject matter pertaining to controlling overload of a transimpedance amplifier in an optical transceiver and/or many of its attendant utilities will be understood by the forgoing description, and it will be apparent that various changes may be made in the form, construction and/or arrangement of the components thereof without departing from the scope and/or spirit of the claimed subject matter or without sacrificing all of its material advantages, the form herein before described being merely an explanatory embodiment thereof, and/or further without providing substantial change thereto. It is the intention of the claims to encompass and/or include such changes.
