Telecommunications – Receiver or analog modulated signal frequency converter – With particular receiver circuit
Reexamination Certificate
2001-05-22
2004-11-02
Nguyen, Simon (Department: 2685)
Telecommunications
Receiver or analog modulated signal frequency converter
With particular receiver circuit
C455S284000, C455S305000, C330S117000, C330S275000, C330S301000
Reexamination Certificate
active
06813486
ABSTRACT:
The invention relates to an RF circuit configured to match an unbalanced port to a balanced port and has particular, but not exclusive, application to radio receivers, transmitters and transceivers, including integrated circuits used to implement radio receivers.
Integrated circuits operating at radio frequencies usually have differential inputs, whereby a two inputs form a balanced pair of inputs to an amplifier. Such inputs should be supplied with signals that are equal in amplitude but 180° out of phase. Many radio frequency (RF) signal sources, such as an antenna, provide a non-differential, unbalanced signal. It is common practice to match such signal sources to such integrated circuits by using a balun to convert an unbalanced signal from an unbalanced signal source to a balanced signal for connection to a balanced pair of inputs. In this application, the basic function of a balun is to generate two versions of the source signal 180° out of phase with respect to each other.
Furthermore, integrated circuits operating at radio frequencies usually have differential outputs, whereby two outputs from a differential output stage form a balanced pair. Such outputs supply signals that are equal in amplitude but 180° out of phase. Many radio frequency (RF) load devices, such as an antenna, require a non-differential, unbalanced signal. It is common practice to match such load devices to such integrated circuits by using a balun to convert a balanced signal pair to an unbalanced signal for connection to an unbalanced load device. In this application, the basic function of the balun is to convert two versions of a signal 180° out of phase with respect to each other to an unbalanced signal by inverting one signal and combining the pair.
Baluns are available as off-the-shelf modules, but these are expensive and generally have quite a high loss.
Baluns can also be implemented using discrete capacitors and inductors, but it is desirable to reduce component count, cost and volume further.
Baluns can be implemented as printed components on a printed circuit board, but would be large at some operating frequencies, for example 2.4 GHz.
An object of the present invention is to provide an improved RF circuit configured to match a balanced port to an unbalanced port.
According to one aspect of the invention there is provided an RF electrical circuit configured to match an unbalanced port to first and second terminals of a balanced port, comprising first and second branches, the first branch comprising a first path coupling the unbalanced port to the first terminal of the balanced port and the second branch comprising a second path coupling the unbalanced port to the second terminal of the balanced port, the first path comprising a first reactive element and the second path comprising a second reactive element, wherein the first reactive element resonates at a first resonant frequency with a first parasitic reactance associated with the first branch, wherein the second reactive element resonates at a second resonant frequency with a second parasitic reactance associated with the second branch, wherein the first resonant frequency is higher than a predetermined operating centre frequency and the second resonant frequency is lower than the predetermined operating centre frequency, and wherein signals delivered to a load from the first and second branches are 180° out of phase with respect to each other.
According to another aspect of the invention there is provided an RF electrical circuit wherein the balanced port comprises an amplifier and the first. and second terminals of the balanced port comprise respectively amplifier first and second inputs, wherein the first branch comprises the amplifier first input and the second branch comprises the amplifier second input, wherein the first reactive element comprises a first inductor having a first inductance and the second reactive element comprises a second inductor having a second inductance, and wherein the first parasitic reactance associated with the first branch comprises an input capacitance of the amplifier first input and the second parasitic reactance associated with the second branch comprises an input capacitance of the amplifier second input.
In one embodiment of the invention there is an input port for receiving an unbalanced signal from a signal source, and an RF amplifier implemented in a CMOS integrated circuit and having a pair of balanced inputs. Two inductors are connected between the input port and the two balanced inputs of the amplifier, one to each input. Each inductor forms a series tuned circuit with the inherent parasitic input capacitance of its respective input of the amplifier. At the resonant frequency of each tuned circuit, the voltage at each respective input changes by 180°. The two inductors have different values such that, at the operating centre frequency of the circuit, one tuned circuit is below resonance and the other resonant circuit is above resonance. In this state, there is a 180° phase difference between the inputs to the amplifier, and the circuit performs the function of a balun.
The input impedance presented to the signal source at the input port is determined by the two inductor values, in conjunction with the internal parasitic resistance of the inductors and the parasitic capacitance of the inputs of the amplifier, and consequently can be set by selection of the resonant frequencies of the two series tuned circuits.
In general, signal sources exhibit a real, not complex, output impedance, and need to be matched with a real load impedance. In order to ensure that the input impedance presented to the signal source at the input port is substantially real, the inductor values are further selected such that the operating centre frequency is substantially midway between the resonant frequencies of the two series tuned circuits.
The value of the input impedance at the input port may be adjusted to achieve a match with the output impedance of the signal source, for example 50&OHgr;, by selection of the difference between the two inductor values, and consequently by selection of the spacing of the resonant frequencies from the operating centre frequency.
In this way, matching of an unbalanced signal source to a balanced pair of inputs to an integrated amplifier is achieved using only two inductors in combination with inherent parasitic characteristics, resulting in low component count, low component cost, and low component volume.
According to a further aspect of the invention there is provided an RF electrical circuit wherein the balanced port comprises an integrated circuit die and the first and second terminals of the balanced port comprise respectively first and second outputs of a differential signal source on respectively first and second connection areas of the integrated circuit die, wherein the first branch comprises the integrated circuit die first output and the second branch comprises the integrated circuit die second output, wherein the first reactive element comprises a first capacitor having a first capacitance and the second reactive element comprises a second capacitor having a second capacitance, wherein the first parasitic reactance associated with the first branch comprises a first parasitic inductance and the second parasitic reactance associated with the second branch comprises a second parasitic inductance.
In a second embodiment of the invention there is an output port for delivering an unbalanced signal to a load device, and a CMOS or bipolar integrated circuit die presenting, on a pair of connection areas, a pair of balanced outputs of a differential signal source. Each of the pair of connection areas is coupled to a respective connection pin of an integrated circuit package by means of a bond wire. A capacitor is coupled between each connection pin and the output port. Each capacitor forms a series tuned circuit with the parasitic inductance inherent in the interconnections of the respective branch; these interconnections encompass integrated circuit die to connection pin, connect
Koninklijke Philips Electronics , N.V.
Nguyen Simon
Waxler Aaron
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