Patent Description:
In a transmitter for optical communications, a broadband driver amplifier is used to increase the level of a high-speed digital source in order to supply enough power to properly drive the electro-optical modulator. In this regard, AC-coupling connection between the high-speed digital source and the driver amplifier is required for decoupling a DC voltage coming from the high-speed digital source.

Driver amplifiers with integrated AC-coupling are of high interest because they drastically reduce module size, number of components and costs. Recently, the updated IEEE <NUM>. 3bs standard requires low cut-off frequency below <NUM>, instead of <NUM> as in old standard. It is thus advantageous to obtain driver amplifiers with integrated input AC-coupling and extended low cut-off frequency, as they allow optical modules to be compliant with new standard.

A typical scheme of a driver amplifier <NUM> adopted in the prior art to achieve AC-coupling is shown in <FIG>. The scheme includes an RC filter composed of <NUM> elements: a resistor RG <NUM> used to provide the proper bias voltage to the driver input; a capacitor CG <NUM> used to decouple the DC voltage coming from the high-speed digital source; and a resistor R<NUM> <NUM> used to provide the proper matched impedance for the high-speed digital source.

The low cut-off frequency ωLCF of the driver amplifier <NUM> in <FIG> can be estimated by using the following equation: <MAT> where RG and CG denote resistance of the resistor <NUM> and capacitance of the capacitor <NUM> respectively.

In view of the above equation, the low cut-off frequency can be extended, i.e. reduced, by either increasing the capacitance or the resistance. Extending the low cut-off frequency by increasing the capacitance of the capacitor CG also reduces the high cut-off frequency ωHCF of the driver amplifier, thus reducing the maximum data-rate supported by the driver amplifier itself. This undesired effect is due to the parasitic capacitance that real integrated metal-insulator-metal (MIM) capacitors have.

<FIG> shows a similar scheme of a driver amplifier <NUM> as in <FIG>, where the capacitor <NUM> CG is realized by means of an integrated MIM capacitor. The MIM capacitor is composed of two metal plates, a top plate <NUM> and a bottom plate <NUM>, and an insulator material (oxide) lies between the two metal plates.

The capacitance between the bottom plate <NUM> and top plate <NUM> realize the capacitor CG <NUM>. However, an integrated driver amplifier has also a ground metal plate <NUM> that generates an undesired capacitance effect to ground with the bottom plate <NUM> of the MIM capacitor. This undesired capacitance effect can be represented by a capacitor CB <NUM> and it is proportional to the MIM capacitor area.

The parasitic capacitor CB <NUM> affects the high cut-off frequency ωHCF of the driver amplifier as shown in the following equation: <MAT> wherein R<NUM> denotes resistance of the resistor R1, CB denotes capacitance of the capacitor CB, RS denotes the output impedance of the high-speed digital source, and CGS denotes the input capacitance of the amplifier block <NUM>.

In order to extend the low cut-off frequency, the area of the MIM capacitor has to be increased, thus increasing the value of the capacitor CG. However, the MIM capacitor area increment also increases the value of the capacitor CB, thus resulting in reduced high cut-off frequency ωHCF.

Another possible solution in a prior-art scheme is to increase the value of the resistor RG. However, this leads to a reliability issue for the driver amplifier. In fact, real transistors composing the amplifier block of the driver amplifier suffer from leakage current from output to input. This leakage current, flowing across the resistor, generates a DC voltage at the input of the amplifier block that increases the output current of the amplifier block itself.

As a consequence, the channel temperature of the transistors composing the amplifier block increases, resulting in reliability and life time risks. As a conclusion, any increase of the resistor, in order to extend the low cut-off frequency, reduces the reliability margin and life-time of the driver amplifier.

Moreover, the previous works do not allow to extend the low cut-off frequency of a driver amplifier without reducing the maximum data-rate or life-time of the driver amplifier itself.

The prior art in form of document <CIT> (<CIT>), document <CIT> (<CIT>), document <CIT> (<CIT>) and document <CIT> (<NUM>-<NUM>-<NUM>) disclose teachings relevant for the field of the present application.

In light of the above, there is still a need for an improved amplifier device for amplifying a signal with a DC signal component more efficiently.

It is an object of the invention to provide an amplifier device, which solves the drawbacks of the prior art. For example, it is an object to provide an amplifier device for amplifying a signal and filtering out a DC component of the signal.

Generally, the present invention relates to an integrated driver amplifier device for amplifying a signal and filtering out a DC component of the signal. Embodiments of the invention allow to extend low cut-off frequency of the driver amplifier that integrates AC-coupled components without reducing high cut-off frequency or reliability margin of the driver amplifier itself.

More specifically, according to a first aspect the invention relates to an amplification device which is configured for amplifying a signal, wherein the signal has a DC signal component. The amplification device comprises: a coupling filter circuit having an input terminal for receiving the input signal and an output terminal for outputting a filtered output signal, wherein the coupling filter circuit is configured to at least attenuate the DC signal component of the input signal to obtain the filtered output signal. The coupling filter circuit comprises: a first capacitor circuit connecting the input terminal to the output terminal, the first capacitor circuit comprising a first capacitor; and a second capacitor circuit connected in parallel to the first capacitor circuit, the second capacitor circuit comprising a second capacitor, a first resistor and a second resistor, wherein the second capacitor, the first resistor and the second resistor are serially connected. The coupling filter circuit further comprises: a resistor circuit connected to the input terminal and the output terminal, the resistor circuit comprising a third resistor connected to the input terminal and a fourth resistor connected to the output terminal. The amplification device further comprises an amplification circuit connected to the output terminal, wherein the amplification circuit is configured to amplify the filtered signal to obtain an amplified filtered signal.

Thus, an improved amplification device is provided, allowing amplifying a signal and filtering out a DC component of the signal.

In a further possible implementation form of the first aspect, the second capacitor circuit is connected in parallel to the first capacitor of the first capacitor circuit.

In a further possible implementation form of the first aspect, the first capacitor circuit is composed only of the first capacitor.

In a further possible implementation form of the first aspect, the second capacitor is connected between the first resistor and the second resistor, wherein the first resistor is directly connected to the input terminal and the second resistor is directly connected to output terminal.

Thus, the low cut-off frequency of the amplification device is reduced without affecting the high cut-off frequency.

In a further possible implementation form of the first aspect, the second capacitor circuit is composed only of the second capacitor, the first resistor and the second resistor.

In a further possible implementation form of the first aspect, the third resistor of the resistor circuit is arranged to couple the input terminal to a reference potential, in particular to a ground potential, and/or the fourth resistor of the resistor circuit is arranged to couple the output terminal to a reference potential, in particular to a ground potential.

Thus, the input terminal and/or the output terminal can be connected to a reference potential respectively.

In a further possible implementation form of the first aspect, the amplification circuit comprises or is formed by a field effect transistor having a gate terminal, wherein the output terminal is connected to the gate terminal.

Thus, the filtered digital signal output from the output terminal can be amplified.

In a further possible implementation form of the first aspect, the amplification device further comprises a further coupling filter circuit, the further coupling circuit being formed identical to the coupling circuit, the coupling circuit and the further coupling circuit being arranged for differential mode operation.

Thus, the coupling filter can be used in applications based on differential signal.

In a further possible implementation form of the first aspect, the amplification device further comprises a further amplification circuit, in particular a further field effect transistor, arranged downstream the further coupling filter circuit.

Thus, the filtered digital signal provided by the further coupling filter circuit can be further amplified.

In a further possible implementation form of the first aspect, the further coupling filter circuit comprises a further input terminal for receiving an inverted version of the input signal, a further output terminal for outputting a further filtered output signal.

The further coupling filter circuit comprises: a further first capacitor circuit connecting the further input terminal to the further output terminal, the further first capacitor circuit comprising a further first capacitor; a further second capacitor circuit connected in parallel to the further first capacitor circuit, the further second capacitor circuit comprising a further second capacitor, a further first resistor and a further second resistor, the further second capacitor, the further first resistor and the further second resistor being serially connected; and a further resistor circuit connected to the further input terminal and the further output terminal, the further resistor circuit comprising a further third resistor connected to the further input terminal and a further fourth resistor connected to the further output terminal. The third resistor of the resistor circuit and the further third resistor of the further resistor circuit are electrically connected, thereby connecting the coupling filter circuit to the further coupling filter circuit.

In a further possible implementation form of the first aspect, the third resistor and the further third resistor are electrically connected at a connection point, wherein the amplification device comprises a shunting capacitor connecting the connection point to a reference potential, in particular to a ground potential.

Thus, the shunting capacitor of the amplification device can shunt a high frequency common-mode.

In a further possible implementation form of the first aspect, the amplification device further comprises a diode circuit comprising a first diode and a second diode, the first diode and the second diode being connected antiparallel to each other, the antiparallel diode circuit connecting the connection point to reference potential, in particular a ground potential.

Thus, the shunting capacitor can be protected from electro-static discharge.

In a further possible implementation form of the first aspect, the respective input terminal is connected via a shunt resistor to a reference potential, in particular to a ground potential.

According to the invention, the respective coupling filter circuit has an electrical bandpass characteristic, with a lower cut-off frequency being equal to <NUM> within a tolerance range, in particular +/- <NUM>% or +/-<NUM>%.

Thus, the respective coupling filter circuit is compliant with the IEEE <NUM>. 3bs standard.

According to the invention, the respective coupling filter circuit comprises integrated capacitors according to the metal-insulator-metal technology. According to a second aspect the invention relates to an optical receiver comprising the amplification device of the first aspect, wherein the optical receiver comprises a converter configured to convert an optical signal into an electrical signal.

Thus, an improved optical receiver is provided, allowing converting an optical signal into an electrical signal more efficiently.

In the various figures, identical reference signs will be used for identical or at least functionally equivalent features.

In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present invention may be placed. It will be appreciated that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present invention is defined by the appended claims.

For instance, it will be appreciated that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa.

Moreover, in the following detailed description as well as in the claims embodiments with different functional blocks or processing units are described, which are connected with each other or exchange signals. It will be appreciated that the present invention covers embodiments as well, which include additional functional blocks or processing units that are arranged between the functional blocks or processing units of the embodiments described below.

Finally, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

As will be described in more detail in the following under reference to <FIG> and <FIG>, embodiments of the invention relate to an amplification device <NUM> which is configured for amplifying a signal that has a DC component to be filtered.

As can be seen from <FIG>, the amplification device <NUM> comprises: a coupling filter circuit <NUM> having an input terminal <NUM> for receiving the input signal and an output terminal <NUM> for outputting a filtered output signal, wherein the coupling filter circuit <NUM> is configured to at least attenuate the DC signal component of the input signal to obtain the filtered output signal.

According to an embodiment, the coupling filter circuit <NUM> comprises: a first capacitor circuit connecting the input terminal <NUM> to the output terminal <NUM>, the first capacitor circuit comprising a first capacitor <NUM>; and a second capacitor circuit connected in parallel to the first capacitor circuit, the second capacitor circuit comprising a second capacitor <NUM>, a first resistor <NUM> and a second resistor <NUM>, wherein the second capacitor <NUM>, the first resistor <NUM> and the second resistor <NUM> are serially connected.

According to an embodiment, the coupling filter circuit <NUM> further comprises: a resistor circuit connected to the input terminal <NUM> and the output terminal <NUM>, the resistor circuit comprising a third resistor <NUM> connected to the input terminal <NUM> and a fourth resistor <NUM> connected to the output terminal <NUM>.

The amplification device <NUM> further comprises an amplification circuit <NUM> connected to the output terminal <NUM>, wherein the amplification circuit <NUM> is configured to amplify the filtered signal to obtain an amplified filtered signal.

<FIG> shows a more general schematic diagram of an integrated coupling filter circuit <NUM> according to an embodiment, wherein the coupling filter circuit <NUM> comprises mainly the following components: two capacitors (CG<NUM> <NUM> and CG<NUM> <NUM>); four resistors (R<NUM> <NUM>, R<NUM> <NUM>, R<NUM> <NUM> and RG <NUM>); an input port <NUM> (IN) and an output port <NUM> (OUT).

As shown in <FIG> and <FIG>, the second capacitor circuit is connected in parallel to the first capacitor <NUM> of the first capacitor circuit and the first capacitor circuit is composed only of the first capacitor <NUM>. Likewise, the second capacitor circuit is composed only of the second capacitor <NUM>, the first resistor <NUM> and the second resistor <NUM>. The second capacitor <NUM> is connected between the first resistor <NUM> and the second resistor <NUM>, and the first resistor <NUM> is directly connected to the input terminal <NUM> and the second resistor <NUM> is directly connected to output terminal <NUM>.

According to an embodiment, the third resistor <NUM> of the resistor circuit is arranged to couple the input terminal <NUM> to a reference potential, in particular to a ground potential, and/or the fourth resistor <NUM> of the resistor circuit is arranged to couple the output terminal <NUM> to a reference potential, in particular to a ground potential. Further, the amplification circuit comprises or is formed by a field effect transistor having a gate terminal, wherein the output terminal is connected to the gate terminal.

According to embodiments of the invention, the low cut-off frequency of the driver amplifier can be extended without reducing the maximum data-rate or life-time of the driver amplifier itself, through a proper choice of the values of the second capacitor CG<NUM> <NUM> and the first resistor R<NUM> <NUM> as well as the second resistor R<NUM> <NUM>. To highlight the benefits, it is convenient to analyze the driver amplifier according to an embodiment in a low frequency range and in a high frequency range, which will be demonstrated in the following under reference to <FIG> and <FIG>.

In the low frequency range, the equivalent impedance of the second capacitor CG<NUM> <NUM> is much higher than the first resistor R<NUM> <NUM> and the second resistor R<NUM> <NUM>. As a consequence, the proposed amplification device shown in <FIG> can be simplified into the amplification device <NUM> shown in <FIG>, wherein the amplification device <NUM> comprises a coupling filter circuit <NUM> and an amplification circuit <NUM>. The resulting low cut-off frequency (ωLCF) of the amplification device <NUM> in <FIG> can be estimated by using the following equation: <MAT>.

Thus, assuming that the first capacitor CG<NUM> <NUM> is equal to the capacitor CG as in <FIG>, the low cut-off frequency (ωLCF) of the proposed amplifier is reduced, i.e. extended, without affecting reliability margin of the driver amplifier by increasing the value of the resistor RG.

In the high frequency range, the equivalent impedance of the first capacitor CG<NUM> <NUM> and the second capacitor CG<NUM> <NUM> is much higher than the first resistor R<NUM> <NUM> and the second resistor R<NUM> <NUM> according to an embodiment. As a consequence, the embodiment shown in <FIG> can be simplified into the amplification device <NUM> shown in <FIG>, wherein the amplification device <NUM> comprises a coupling filter circuit <NUM> and an amplification circuit <NUM>. The resulting high cut-off frequency (ωHCF) of the amplification device <NUM> in <FIG> can be estimated by using the following equation: <MAT> wherein CB<NUM> denotes the parasitic capacitor <NUM> to ground of the first capacitor CG<NUM> <NUM>. From the above equation, it is to be noted that the parasitic capacitor to ground (CB<NUM>) of the second capacitor CG<NUM> <NUM> does not affect the high cut-off frequency of the amplification device <NUM>.

To further demonstrate the benefits of the amplification device according to embodiments of the invention, a numerical example will be discussed in the following.

It is assumed that a driver amplifier is designed to achieve a low cut-off frequency of <NUM> and a high cut-off frequency of <NUM>. The resulting values of capacitors and resistors in a prior art driver amplifier are as follows: RS, R<NUM>, and RG are <NUM> Ohm, <NUM> Ohm and <NUM> KOhm respectively; CG, CB and CGS are <NUM> pF, 32fF and 110fF respectively, wherein it is assumed that the parasitic capacitor to ground of the MIM capacitor (CB) is hundred times lower than the MIM capacitor value (CG). Moreover, an input capacitance of 110fF is assumed for the amplifier block. Finally, the output impedance of the source (RS) is assumed to be <NUM> Ohm.

By using the aforementioned equations in the background section, it is possible to derive <NUM> as low cut-off frequency and <NUM> as high cut-off frequency. It is now required to extend the low cut-off frequency of the driver amplifier to <NUM> in order be compliant with new standard, without affecting reliability margin of the driver amplifier.

By using the prior art scheme, the only solution is to increase the MIM capacitor value (i.e. CG=<NUM>. 6pF), wherein RS, R<NUM>, and RG are <NUM> Ohm, <NUM> Ohm and <NUM> KOhm respectively; CG, CB and CGS are <NUM> pF, 106fF and 110fF respectively.

However, the parasitic capacitor to ground (CB) also increases, resulting in a reduced high frequency cut-off which is equal to <NUM>.

On the contrary, the low cut-off frequency can be extended without affecting the high cut-off frequency for the embodiments of the invention. In fact, it is possible to select proper values for the second capacitor CG<NUM> and the first resistor R<NUM> <NUM> as well as the second resistor R<NUM> <NUM> as follows: RS, R<NUM>, and RG are <NUM> Ohm, <NUM> Ohm and <NUM> KOhm respectively; CG, CB and CGS are <NUM> pF, 32fF and 110fF respectively; R<NUM>, R<NUM>, CG<NUM>, and CB<NUM> are <NUM> KOhm, <NUM> KOhm, <NUM> pF and <NUM> fF respectively.

By using the above equations as discussed along with <FIG> and <FIG>, it is possible to find that the low cut-off frequency of the amplification device is extended to <NUM>, while the high cut-off frequency is kept as the original case, i.e. equal to <NUM>.

According to a further embodiment, <FIG> shows a schematic diagram of an exemplary amplification device <NUM>, which can be used in differential-mode. As can be taken in a close view from <FIG>, the amplification device <NUM> further comprises a coupling filter circuit <NUM> and a further coupling filter circuit <NUM>, wherein the further coupling circuit <NUM> is formed identical to the coupling filter circuit <NUM>, and the coupling filter circuit <NUM> and the further coupling filter circuit <NUM> are arranged for differential mode operation.

In an embodiment, the amplification device <NUM> further comprises a further amplification circuit, in particular a further field effect transistor, arranged downstream the further coupling filter circuit <NUM>.

As in <FIG> and <FIG>, the coupling filter circuit <NUM> comprises: a first capacitor circuit connecting the input terminal <NUM> to the output terminal <NUM>, the first capacitor circuit comprising a first capacitor <NUM>; and a second capacitor circuit connected in parallel to the first capacitor circuit, the second capacitor circuit comprising a second capacitor <NUM>, a first resistor <NUM> and a second resistor <NUM>, wherein the second capacitor <NUM>, the first resistor <NUM> and the second resistor <NUM> are serially connected. According to an embodiment, the coupling filter circuit <NUM> further comprises: a resistor circuit connected to the input terminal <NUM> and the output terminal <NUM>, the resistor circuit comprising a third resistor <NUM> connected to the input terminal <NUM> and a fourth resistor <NUM> connected to the output terminal <NUM>.

In a further embodiment, the further coupling filter circuit <NUM> comprises a further input terminal <NUM> for receiving an inverted version of the input signal, a further output terminal <NUM> for outputting a further filtered output signal.

The further coupling filter circuit <NUM> comprises: a further first capacitor circuit connecting the further input terminal <NUM> to the further output terminal <NUM>, the further first capacitor circuit comprising a further first capacitor <NUM>; a further second capacitor circuit connected in parallel to the further first capacitor circuit, wherein the further second capacitor circuit comprises a further second capacitor <NUM>, a further first resistor <NUM> and a further second resistor <NUM>. The further second capacitor <NUM>, the further first resistor <NUM> and the further second resistor <NUM> are serially connected.

In an embodiment, the further coupling filter circuit <NUM> also comprises: a further resistor circuit connected to the further input terminal <NUM> and the further output terminal <NUM>, the further resistor circuit comprising a further third resistor <NUM> connected to the further input terminal <NUM> and a further fourth resistor <NUM> connected to the further output terminal <NUM>.

As seen in <FIG>, the third resistor <NUM> of the resistor circuit and the further third resistor <NUM> of the further resistor circuit are electrically connected, thereby connecting the coupling filter circuit <NUM> to the further coupling filter circuit <NUM>.

<FIG> shows a schematic diagram of an exemplary amplification device <NUM> according to an embodiment, where a capacitor (C1) is added into the amplification device <NUM> as shown in <FIG> in order to shunt a high frequency common-mode. Similar to the amplification device <NUM> in <FIG>, the amplification device <NUM> comprises a coupling filter circuit <NUM> and a further coupling filter circuit <NUM>, wherein the further coupling circuit <NUM> is formed identical to the coupling filter circuit <NUM>.

In particular, the third resistor <NUM> and the further third resistor <NUM> are electrically connected at a connection point, wherein the amplification device <NUM> comprises a shunting capacitor <NUM> connecting the connection point to a reference potential, in particular to a ground potential.

<FIG> shows a schematic diagram of an exemplary amplification device <NUM> according to an embodiment, where two diodes, a first diode <NUM> and a second diode <NUM>, are added into the amplification device <NUM> as shown in <FIG> in order to protect the shunting capacitor <NUM> from electro-static discharge.

Similar to the amplification device <NUM> in <FIG> or the amplification device <NUM> in <FIG>, the amplification device <NUM> also comprises a coupling filter circuit <NUM> and a further coupling filter circuit <NUM>, wherein the further coupling circuit <NUM> is formed identical to the coupling filter circuit <NUM>.

In an embodiment, the amplification device <NUM> comprises a diode circuit comprising a first diode <NUM> and a second diode <NUM>, wherein the first diode <NUM> and the second diode <NUM> are connected antiparallel to each other, the antiparallel diode circuit connecting the connection point to reference potential, in particular a ground potential.

In an embodiment, the respective input terminal is connected via a shunt resistor to a reference potential, in particular to a ground potential.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

Claim 1:
Amplification device (<NUM>) configured for amplifying a signal, the amplification device (<NUM>) comprising:
a coupling filter circuit (<NUM>) having an input terminal (<NUM>) for receiving the input signal, an output terminal (<NUM>) for outputting a filtered output signal, wherein the coupling filter circuit (<NUM>) is configured to at least attenuate a DC signal component of the input signal to obtain the filtered output signal, wherein the coupling filter circuit (<NUM>) comprises
- integrated capacitors according to metal-insulator-metal technology;
- a first capacitor circuit connecting the input terminal (<NUM>) to the output terminal (<NUM>), the first capacitor circuit comprising a first capacitor (<NUM>);
- a second capacitor circuit connected in parallel to the first capacitor circuit, the second capacitor circuit comprising a second capacitor (<NUM>), a first resistor (<NUM>) and a second resistor (<NUM>), the second capacitor (<NUM>), the first resistor (<NUM>) and the second resistor (<NUM>) being serially connected; and
- a resistor circuit connected to the input terminal (<NUM>) and the output terminal (<NUM>), the resistor circuit comprising a third resistor (<NUM>) connected to the input terminal (<NUM>) and a fourth resistor (<NUM>) connected to the output terminal (<NUM>); wherein the coupling filter circuit (<NUM>) is configured to have an electrical bandpass characteristic, with a lower cut-off frequency being equal to <NUM> within a tolerance range, in particular +/- <NUM>% or +/-<NUM>%, by selecting proper values for the second capacitor, the first resistor and the second resistor; and
an amplification circuit (<NUM>) connected to the output terminal (<NUM>), the amplification circuit (<NUM>) being configured to amplify the filtered signal to obtain an amplified filtered signal.