WO2009060264A1

WO2009060264A1 - Integrated circuit having harmonic termination circuitry

Info

Publication number: WO2009060264A1
Application number: PCT/IB2007/055383
Authority: WO
Inventors: Cedric Cassan; Michael Watts
Original assignee: Freescale Semiconductor, Inc.
Priority date: 2007-11-08
Filing date: 2007-11-08
Publication date: 2009-05-14

Abstract

A semiconductor device comprises harmonic termination circuitry (300) for providing harmonic termination on an output path (310) from an output (320) of an active component (305) of an amplifier circuit, the harmonic termination circuitry (300) comprising a third harmonic resonant circuit (340). The third harmonic resonant circuit (340) substantially couples the output path (310) to ground, and is arranged to provide an impedance substantially representative of a short circuit between the output path (310) and ground at a third harmonic frequency. The harmonic termination circuitry (300) further comprises impedance transformer circuitry (350), provided in series along the output path (310) between the output (320) of the active component (305) and the third harmonic resonant circuit (340), the impedance transformer circuitry (350) arranged to transform a zero impedance, provided by the third harmonic resonant circuit (340) at the third harmonic frequency, into an infinite impedance at the third harmonic frequency, as perceived by the output (320) of the active component (305).

Description

INTEGRATED CIRCUIT HAVING HARMONIC TERMINATION CIRCUITRY

Field of the Invention

The field of the invention generally relates generally to power amplifiers having harmonic termination circuitry. In particular, embodiments of the invention relate to improved on-chip harmonic terminations for class 'F' power amplifiers.

Background of the Invention

In the field of this invention, manufacturers of power amplifiers (PA's), and communication units arranged to use power amplifiers, are constantly aiming to design high efficiency topologies capable of providing high performances within the saturation region of class 'F' power amplifiers. This is of particular importance within existing Gaussian Minimum Shift Keying (GMSK) modulation-based communication systems and associated wireless communication units, such as Global System for Mobile (GSM) communications telephone handsets and the like.

Harmonic termination (or class-F) is a well-known theory to improve radio frequency (RF) Power Amplifier (PA) efficiency. This theory describes idealised operating conditions that designers aim to achieve in practical RF PA circuits. Many circuit topologies have been proposed in numerous technical papers to overcome the known design problem to be as close as possible to the theoretical harmonic impedances by minimizing parasitic effects and dependency of external environment.

Typically, power amplifier integrated circuits (PAICs) are manufactured by semiconductor device manufacturers, and then purchased by, for example, wireless communication unit manufacturers. The wireless communication unit manufacturers often re-design the input and output matching networks of their transmitter to accommodate their particular systems. In an harmonic matched RF power amplifier, it is necessary to have the harmonic termination inside the PAIC, as this allows the harmonic terminations to be more effective as they are closer to the active device. Moreover, it provides some ease of use to users of the PAIC (e.g. device manufacturers using the PAIC) as they do not have to set the harmonic terminations externally. Consequently, in order to be able to guarantee a given level of performance, irrespective of the external matching, and for ease of use, the harmonic terminations are required to be set inside the package and made insensitive to the external matching.

Many papers have already described the advantages of presenting suitable impedances at the harmonics to improve the efficiency of the active component, which for class 'F' power amplifiers typically is in the form of a microwave transistor. The improvement in efficiency brought about by presenting suitable impedances at the harmonics is such that it is of considerable interest within the wireless telecommunications industry.

The principle of the class 'F' type of operation is to present a second harmonic 'short' circuit and a third harmonic 'open' circuit to the microwave transistor's current source. FIG. 1 illustrates a known topology 100 of an on-chip harmonic termination for a class 'F' power amplifier.

The power amplifier design comprises an active component in a form of a transistor 105. A second harmonic resonant circuit 110 is coupled between the drain of the transistor 105 and ground. The second harmonic resonant circuit 110 comprises inductance 115 coupled in series with capacitance 120. A third harmonic resonant circuit 130 is coupled in series between the drain of the transistor 105 and an output 150 of the amplifier. The third harmonic resonant circuit 130 comprises inductance 135 coupled in parallel with capacitance 140.

As will be appreciated by a skilled artisan, the second harmonic resonant circuit 110 acts as a band-pass filter having substantially zero impedance at a resonant frequency of the circuit, namely at the second harmonic frequency. Conversely, the third harmonic resonant circuit 130 acts as a band-stop filter having substantially infinite impedance at the resonant frequency of the circuit, namely at the third harmonic frequency.

This topology works well with ideal components, and is relatively insensitive to any external tuning so long as such ideal components are used. However, in practice such a circuit is very difficult to implement. FIG. 2 illustrates a known problem that designers face when implementing the topology of FIG. 1.. This known topology relies on the fact that the series inductance 135 of the third harmonic resonant circuit 130 has to be as lossless as possible. A relatively simple way to make a low loss inductance is to use a wire bond. In this case, transmission lines have to be added on each side of the series, parallel capacitance 140 of the third harmonic resonant circuit 130 to connect the two wire bond pads of the series wire. Thus, the resulting third harmonic circuit is no longer resonant at the desired frequency, due to the presence of the transmission lines 205.

These transmission lines act as extra series inductance and shunt capacitance put in series with the original series capacitor 140. Therefore, the parallel inductance 135 is unable to resonate the series capacitance 140 any more, due to the presence of transmission lines 205. Thus, the resulting third harmonic impedance presented to the active device 105 is not high enough to be independent of the external tuning (not shown), which as mentioned above is problematic since it is ultimately dependent upon the wireless communication unit manufacturer's, specific implementation. For example, any variation or poor component tolerance on the external matching circuit (external to the PAIC) is likely compromise the performance of the power amplifier. Consequently, an inability for a PAIC manufacturer to guarantee a given level of performance, irrespective of the external matching employed by the end user, significantly impedes the development of substantially generic power amplifier integrated circuits. Such a limitation is restrictive on device manufacturers, for example wireless communication unit manufacturers, with regard to implementing devices comprising power amplifier integrated circuits.

Thus, a need exists for an integrated circuit for a power amplifier having improved harmonic termination circuitry.

Summary of Invention

In accordance with aspects of the invention, there is provided an integrated circuit comprising harmonic termination circuitry, and a communication unit comprising such an integrated circuit, as defined in the appended Claims.

Brief Description of the Drawings

FIG. 1 and FIG. 2 illustrate a known topology and implementation of an on-chip harmonic termination for a class 'F' power amplifier.

Exemplary embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 3 illustrates harmonic termination circuitry, adapted in accordance with an embodiment of the invention;

FIG. 4 illustrates a more detailed description of the harmonic termination circuitry of FIG. 3.

FIG. 5 illustrates an example of an implementation of the harmonic termination circuitry of FIG. 4.

FIG. 6 illustrates a Smith Chart representation highlighting advantages resulting from employing embodiments of the invention.

FIG. 7 illustrates a semiconductor device, adapted in accordance with an embodiment of the invention. - A -

FIG. 8 illustrates a graph showing power added efficiency performance versus input power of conventional class 'F' power amplifier provided with both known termination circuitry and harmonic termination circuitry in accordance with the embodiment of the invention illustrated in FIGs. 3 to 5.

Description of Embodiments

Embodiments of the invention will be described in terms of an on-chip class 'F' radio frequency (RF) power amplifier and harmonic termination circuitry therefor. However, it will be appreciated by a skilled artisan that the inventive concept herein described may be embodied in any type of amplifier design in which harmonic termination is required. For example, it is envisaged that the inventive concept described herein may equally be applied to power amplifier and harmonic termination circuitry not provided 'on-chip'.

Harmonic termination circuitry is described for providing harmonic termination on an output path of an active component of an amplifier circuit in an attempt to provide a particular level of performance, irrespective of the external matching, harmonic termination circuitry comprising a third harmonic resonant circuit coupling the output path of an active component to ground, The harmonic termination circuitry is arranged to provide an impedance representative of a short circuit between the output path and ground at a third harmonic frequency. The harmonic termination circuitry further comprises impedance transformer circuitry, provided in series located between the output of the active component and the third harmonic resonant circuit. The impedance transformer circuitry is arranged to transform a zero impedance, provided by the third harmonic resonant circuit at the third harmonic frequency, into an infinite impedance at the third harmonic frequency, as perceived at the output of the active component. It will be apparent that the term 'infinite impedance' is to be construed as an impedance which in the specific implementation can be considered as being infinite.

Referring now to FIG. 3, there is illustrated a generic block diagram of harmonic termination circuitry 300 according to some embodiments of the invention. The harmonic termination circuitry 300 provides harmonic termination on an output path 310 from an output 320 of an active component 305 of an amplifier circuit (not shown). The harmonic termination circuitry 300 comprises a second harmonic resonant circuit 330, coupled between the output 320 of the active component 305 and ground, and arranged to provide an impedance substantially representative of a short circuit between the output 320 of the active component 305 and ground at a second harmonic frequency.

In accordance with embodiments of the invention, the harmonic termination circuitry 300 further comprises a third harmonic resonant circuit 340, coupled between the output path 310 and ground, and arranged to provide an impedance substantially representative of a short circuit between the output path 310 and ground at a third harmonic frequency. The harmonic circuitry 300 further comprises impedance transformer circuitry 350, provided in series along the output path 310 between the output 320 of the active component 305 and the third harmonic resonant circuit 340, the impedance transformer circuitry 350 is arranged to transform a substantially zero impedance, provided by the third harmonic resonant circuit 340 at the third harmonic frequency, into a substantially infinite impedance at the third harmonic frequency, as perceived by the output 320 of the active component 305.

As will be appreciated by a skilled artisan, by providing an impedance substantially representative of a short circuit between the output path and ground at the third harmonic frequency, and transforming the impedance as perceived by the output of the active component from substantially zero to substantially infinite at the third harmonic frequency, external tuning has substantially no effect on the load impedance perceived by the output of the active component at the third harmonic frequency. Consequently, a level of performance provided by the amplifier circuit may be substantially assured, irrespective of the external matching employed.

In this manner, development of power amplifier integrated circuits (PAICs) suitable for implementation within a diverse range of radio frequency devices, such as wireless communication units, may be facilitated, and the use of such PAICs may be less restrictive on device manufacturers, for example wireless communication unit manufacturers, due to the substantially less sensitive characteristics required in terms of external matching, as compared to prior art harmonic termination techniques.

Referring now to FIG. 4, there is illustrated harmonic termination circuitry 400 according to an embodiment of the invention. The harmonic termination circuitry 400 provides harmonic termination on an output path 410 from an output of an active component of an amplifier circuit. For the embodiment illustrated in FIG. 4, the active component is shown as an equivalent circuit 405 of a microwave transistor for ease of explanation and drain 420 of the microwave transistor 405 provides the output of the active component.

The harmonic termination circuitry 400 comprises a second harmonic resonant circuit 430, coupled between the drain 420 of the microwave transistor 405 and ground. The second harmonic resonant circuit 430 comprises an inductance 435 and a capacitance 437 in series, and arranged to provide an impedance substantially representative of a short circuit between the drain 420 of the microwave transistor 405 and ground at a second harmonic frequency.

The harmonic termination circuitry 400 further comprises a third harmonic resonant circuit 440, coupled between the output path 410 and ground. The third harmonic resonant circuit 440 comprises an inductance 445 and a capacitance 447 in series, and arranged to provide an impedance substantially representative of a short circuit between the output path 410 and ground at a third harmonic frequency.

The harmonic termination circuitry 400 still further comprises impedance transformer circuitry 460, provided in series along the output path 410 between the drain 420 of the microwave transistor 405 and the third harmonic resonant circuit 440. The impedance transformer circuitry 460 is represented as a combination of shunt capacitor Cds, series inductance 450 and series LC circuit

430 arranged to transform a substantially zero impedance, provided by the third harmonic resonant circuit 440 at the third harmonic frequency, into a substantially infinite impedance at the third harmonic frequency, as perceived by the drain 420 of the microwave transistor 405.

This impedance inverter is based on the quarter wave length line effect, as described below. It is envisaged that the impedance inverter may be realized using lumped series inductances and lumped shunt capacitances put in series (discrete components or fully integrated lumped elements). It is also envisaged, for example, that the impedance inverter may be realized using a transmission line which length equals a quarter wave at the desired third harmonic frequency. It is further envisaged, for example, that the impedance inverter may be realized using a wire bond to perform the series inductance role combined with shunt capacitors. It is also envisaged, for example, that the shunt capacitors may be lumped components (added inside the package) or existing capacitors (Cds of the active device and/or capacitor of the second harmonic termination circuit 430).

As will be appreciated by a skilled artisan, standing waves at resonant frequency points of a short- circuited transmission line produce certain effects, in particular when the frequency is such that exactly a quarter wavelength, or some multiple thereof, matches the length of the transmission line. More particularly, when the frequency is such that a quarter wavelength, or some odd multiple thereof, matches the length of the transmission line, the transmission line acts as an impedance transformer, transforming an infinite impedance into zero impedance and vice versa. Thus, when the length of the transmission line is equal to a quarter of the wavelength of the frequency, or an odd multiple thereof, a short circuit (effectively comprising zero impedance) at one end of the transmission line will be transformed into an open circuit, as perceived by the other end of the transmission line, for that particular frequency.

Referring back to FIG. 4, as previously mentioned, the third harmonic resonant circuit 440 is arranged to provide an impedance substantially representative of a short circuit between the output path 410 and ground at a third harmonic frequency. Additionally, the impedance transformer circuitry 460 is arranged to transform a substantially zero impedance, provided by the third harmonic resonant circuit 440 at the third harmonic frequency, into a substantially infinite impedance at the third harmonic frequency, as perceived by the drain 420 of the microwave transistor 405. Accordingly, the output path 410 between the drain 420 and the third harmonic resonant circuit 440 is required to act as a transmission line comprising a length substantially equal to a quarter wavelength of the desired frequency, namely the third harmonic frequency, or odd multiple thereof. Thus, the series inductance (450) of the impedance transformer circuitry (460), The Cds of the active device (405), the inductance (435) and capacitance (437) value of the second harmonic termination (430) are arranged to substantially match the impedance of the output path 410, between the drain 420 and the third harmonic resonant circuit 440, to that of a transmission line comprising a length substantially equal to a quarter, or odd multiple thereof, of the third harmonic frequency wavelength.

Referring now to FIG. 5, there is illustrated an example of an implementation 500 of the harmonic termination circuitry 400 of FIG. 4, where the harmonic termination circuitry forms a part of a power amplifier integrated circuit (not shown). The second and third harmonic resonant circuits 430, 440 are integrated on a die comprising a high resistivity type of substrate, such as gallium arsenide (GaAs) or high resistivity silicon. The drain 420 of the microwave transistor 405 and the second harmonic resonant circuit 430 are coupled to a first contact pad 510, and the third harmonic resonant circuit 440 is coupled to a second contact pad 520. The first and second contact pads 510, 520 may be made of any suitable material, for example gold.

The impedance transformer circuitry, which includes a series inductance 450, comprises a wire bond, the ends of which are attached to the first and second contact pads 510, 520, for example by way of ball bonding or wedge bonding. The wire bond may comprise any suitable material, for example gold. The second contact pad 520 is further coupled to a package lead of the power amplifier integrated circuit. Thus, in this embodiment, only the wire bond couples the output of the radio frequency power amplifier to one end of the third harmonic termination circuitry, thereby facilitating more accurate design to ensure the impedance transformation represents an infinite impedance at an power amplifier and a zero impedance at the third harmonic termination circuitry.

Referring now to FIG. 6, there is illustrated a Smith Chart representation 600 highlighting the advantages provided by the aforementioned embodiments. The Smith Chart representation 600 illustrates the third harmonic impedance, as perceived by the drain of a microwave transistor when the impedance at the third harmonic frequency is varied outside the package, for example due to variations in external tuning, where the output path is provided with known harmonic termination circuitry in Smith Charge 610 and where the output path is provided with harmonic termination circuitry according to the embodiment illustrated in FIG's. 3 to 5 in Smith Chart 620.

As can be seen, the third harmonic impedance at a frequency of 2.82 GHz is less sensitive, as perceived by the drain of the microwave transistor, when provided with harmonic termination circuitry according to the embodiment illustrated in FIGs. 3 to 5, as compared to the prior art harmonic termination circuitry throughout the impedance variation range at this frequency. For the results illustrated in FIG. 6, the real part of the third harmonic impedance variation for the prior art harmonic termination circuitry is five times greater than that for the harmonic termination circuitry according to the embodiment illustrated in FIGs. 3 to 5.

Referring now to FIG. 7, there is illustrated a semiconductor device 700, for example a power amplifier integrated circuit, comprising a power amplifier 705 and harmonic termination circuitry 710 according to an embodiment of the invention. Also illustrated in FIG. 7 are input and output matching networks 720, 730.

In one embodiment of the invention, it is envisaged that the harmonic termination circuitry 710 may be integrated on the same die as the power amplifier 705, of which the active component forms a part, where the die may comprise a high resistivity substrate. This integration allows for the second harmonic resonant circuit of the harmonic termination circuitry 710 to be connected substantially directly to the drain output of the active component of the power amplifier 705, substantially without a need for additional elements to be provided there between. In this manner, the short circuit effect at the second harmonic frequency may be substantially maximised. Moreover, monolithic integrated circuit approach allows for impedance transformer circuitry, for example a wire bond, to be bonded on the die, thereby minimising assembly variations. In addition, the cost of such an approach is advantageously low compared to multi die techniques.

Referring now to FIG. 8, there is illustrated a graph 800 showing power added efficiency (PAE) performance 810 versus input power (Pin) 805 for conventional class 'F' (CCF) power amplifiers provided with harmonic termination circuitry. The graph 800 illustrates a performance of known harmonic termination circuitry 820 with a performance of harmonic termination circuitry 815 according to embodiments of the invention. As can be seen, the dispersion of PAE in the saturation region is over five times less for the CCF with harmonic termination circuitry in accordance with the embodiment of the invention 815 than for the CCF with the prior art harmonic termination circuitry 820. Furthermore, the absolute PAE value is advantageously higher.

It will be understood that the integrated circuit with improved harmonic termination circuitry, as described above, aims to provide at least one or more of the following advantages:

(i) The harmonic termination circuitry impedance is independent of any external tuning at the second and third harmonic frequency. (ii) A Quarter-wave length line is easily realized with a wire bond, in a very simple manner, which is an easy assembly technique to introduce during manufacturing.

(iii) The two series LC resonant circuits can be easily integrated in a die. This is a key advantage for monolithic RF PA IC components (with a high 'Q' cap IC process) and provides good reproducibility due to a low dispersion of component values (compared to discrete parts). (iv) As the harmonic termination circuitry is independent of the external environment, higher PAE performances can be achieved with low dispersion. This technique will thus, improve a yield performance from a manufacturability point of view.

(v) When implemented with real components (with losses), the harmonic termination circuitry is insensitive to any external tuning.

It will be appreciated that any suitable distribution of functionality between different functional units may be used without detracting from the inventive concept herein described. Hence, references to specific functional devices or elements are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit or IC, in a plurality of units or ICs or as part of other functional units.

In particular, it is envisaged that the aforementioned inventive concept can be applied by a semiconductor manufacturer to any integrated circuit comprising a power amplifier requiring harmonic termination. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device or application-specific integrated circuit (ASIC) and/or any other sub-system element.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term 'comprising' does not exclude the presence of other elements or steps.

Furthermore, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate. Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to 'a', 'an' , 'first' , 'second', etc. do not preclude a plurality. The term "coupled," as used herein, is not intended to be limited to a direct coupling.

Thus, an integrated circuit with improved harmonic termination circuitry for a power amplifier has been described where the aforementioned disadvantages with prior art arrangements have been substantially alleviated.

Claims

Claims (PCT)

1. A semiconductor device comprising harmonic termination circuitry (400) for providing harmonic termination on an output path (410) of a radio frequency power amplifier, the harmonic termination circuitry (400) comprising:a third harmonic resonant circuit (440);

the third harmonic resonant circuit (440) being arranged to couple the output path (410) to ground, and arranged to provide an impedance representative of a short circuit between the output path (410) and ground at a third harmonic frequency; and the harmonic termination circuitry (400) further comprising impedance transformer circuitry (450), provided in between the output of the radio frequency power amplifier (405) and the third harmonic resonant circuit (440), the impedance transformer circuitry (450) being arranged to transform a zero impedance, provided by the third harmonic resonant circuit (440) at the third harmonic frequency, into an infinite impedance at the third harmonic frequency, as perceived by the output (420) of the radio frequency amplifier (405).

2. The semiconductor device of Claim 1 , wherein the radio frequency power amplifier comprises a microwave transistor (405), and the impedance transformer circuitry (450) is arranged to transform a zero impedance into an infinite impedance as perceived at a drain (420) of the microwave transistor (405).

3. The semiconductor device of Claim 1 or Claim 2 wherein the third harmonic resonant circuit (440) comprising an inductance (445) and a capacitance (447) in series.

4. The semiconductor device of any preceding Claim wherein the impedance transformer circuitry comprising an arrangement of a series inductance (450), a shunt inductance (435) and shunt capacitances (437, 405).

5. The semiconductor device of any preceding Claim wherein the series inductance (450), a shunt inductance (435) and shunt capacitances (437, 405) being arranged to represent a quarter wavelength transmission line, or multiple thereof, of the third harmonic frequency wavelength.

6. The semiconductor device of any preceding Claim wherein the third harmonic resonant circuit (440) is integrated on a same die as the radio frequency power amplifier.

7. The semiconductor device of any preceding Claim wherein the impedance transformer circuit (460) is integrated on a same die as the radio frequency power amplifier.

8. The semiconductor device of any of preceding Claims 1 to 3 wherein the series inductance (450) of the impedance transformer circuitry (460) comprises a wire bond.

9. A radio frequency device comprising the semiconductor device of any of the preceding Claims.

10. The radio frequency device of Claim 9 wherein the device is a wireless communication unit.