Telecommunications – Receiver or analog modulated signal frequency converter – With wave collector
Reexamination Certificate
1998-11-30
2001-08-14
Vo, Nguyen T. (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
With wave collector
C455S323000, C330S296000
Reexamination Certificate
active
06275687
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a low-noise amplifier circuit and mixer. More particularly, the invention relates to a circuitry for a radio frequency receiver of a cellular phone.
BACKGROUND OF THE INVENTION
A typical receiver for a radio frequency signal (RF signal) comprises a combination of an amplifier and a mixer for signal amplification and frequency conversion. The amplifier, usually a low-noise amplifier (LNA), receives the RF signal, amplifies the RF signal and feeds the amplified RF signal to the mixer which in addition receives a local signal from a local oscillator (LO). The local oscillator signal has a frequency which is different from the frequency of the RF signal. The mixer, which is a nonlinear device, generates an output signal that includes more frequencies than the frequencies of the RF signal and the local signal. The output signal is usually filtered to block undesired frequencies which include the original frequencies, their harmonics and their sum frequencies.
The amplifier and mixer used in such a receiver should ideally exhibit several desired parameters and characteristics which are usually used to describe the performance of the amplifier and the mixer. For example, an amplifier should exhibit a high power gain, a low noise figure and the capability of handling large input signals without intermodulation distortion (IMD). The power gain is defined as the ratio of the signal power at the output port to the signal power at the input port. The noise figure is defined as the ratio of the signal-to-noise ratio (SNR) at the input port to the signal-to-noise ratio at the output port.
The intermodulation distortion refers to undesired frequency components which are caused when a signal having two or more sinusoidal frequencies f
1
, f
2
is applied to a nonlinear amplifier. The output signal of such an amplifier contains the additional undesired frequency components called intermodulation products. The output signal will contain, for example, frequency components at DC, f
1
, f
2
, 2f
1
, 2f
2
, 3f
1
, 3f
2
, f
1
+/−f
2
, 2f
1
+/−f
2
and 2f
2
+/−f
1
. The frequencies 2f
1
and 2f
2
are the second harmonics, 3f
1
, and 3f
2
are the third harmonics, f
1
+/−f
2
are the second-order intermodulation products (the sum is 2), and 2f
1
+/−f
2
and 2f
2
+/−f
1
are the third-order intermodulation products (the sum is 3). The third-order intermodulation products are close to the fundamental frequencies f
1
and f
2
and fall within a bandwidth in which the amplifier amplifies, producing distortion in the output signal.
A parameter to evaluate the third-order intermodulation products is the so-called third-order intercept point (IP3). This point is defined by means of a graphical analysis using the output power of the third-order intermodulation product as a function of the input power and the output power of the fundamental component at fl as a function of the input power. The intercept point is defined as the point at which the two (linearized) graphs intercept. The higher the intercept point, the better the suppression of the third-order intermodulation product and the less disturbed is the output signal of the amplifier.
The mixer should exhibit, inter alia, a high conversion gain, a low noise figure and also a high third-order intercept point (IP3). The conversion gain is defined as the ratio of the output power of the IF signal to the input power of the RF signal.
The combination of the LNA amplifier and the mixer is configurable to operate in receivers which are adapted for various applications. For example, the combination can be used in TV receivers or in phones for a radio communications system. One example of a radio communications systems is a cellular system that is in accordance with a particular standard, such as “Global System for Mobile Communications” (GSM), “Advanced Mobile Phone System” (AMPS) or “Code Division Multiple Access” (CDMA).
These standards have different requirements and specifications for the combination of the LNA amplifier and the mixer, for example, with respect to linearity, noise figure and intermodulation distortions. Particularly the CDMA standard requires that the LNA amplifiers and mixers in CDMA phones have simultaneously both a high IP3 and a low noise figure.
To achieve this combination of difficult specifications, current solutions implement circuit architectures, including RF transistors (SFET, HBT), in gallium arsenide (GaAs) technology. Processes to manufacture the circuits and the RF transistors in GaAs technology, however, are expensive compared to processes in silicon technology.
SUMMARY OF THE INVENTION
There is, therefore, a need to provide an LNA amplifier and a mixer which fulfill the specifications, for example, defined for hand-held communications devices, and can be implemented in low-cost silicon technology.
An aspect of the invention relates to a hand-held communications device, for example, a cellular phone or a wireless phone. The hand-held communications device includes a mixer, an amplifier module and an interface circuit. The mixer is configured to receive a first signal having a first frequency and a second signal having a second frequency, and to output a third signal which is a function of the first and second signals. The amplifier module includes a first amplifier stage and a second amplifier stage and is configured to amplify a communications signal which is then input into the mixer as the first signal. The first and second amplifier stages are in communication via a first signal path and a second signal path. The interface circuit is interposed between the mixer and the amplifier module, and inserted into the second signal path so that a direct current (DC) bias current flows from the first amplifier stage through the interface module into the second amplifier stage.
A further aspect of the invention relates to an apparatus for generating an intermediate signal. The apparatus includes a mixer, a circuit module and an interface circuit. The mixer is configured to receive a first signal having a first frequency and a second signal having a second frequency, and to output a third signal which is a function of the first and second signals. The circuit module includes a first circuit stage and a second circuit stage and is configured to modify a communications signal which is input into the mixer as the first signal. The first and second circuits are in communication via a first signal path and a second signal path. The interface circuit is interposed between the mixer and the circuit module, and inserted into the second signal path so that a bias current flows between the first circuit and the second circuit via the interface module.
An other aspect of the invention relates to an apparatus for amplifying an electrical signal. The apparatus includes an amplifier module, and an interface circuit. The amplifier module comprises a first amplifier stage and a second amplifier stage and is configured to amplify the electrical signal. The first and second amplifier stages are in communication via a first signal path and a second signal path. The interface circuit is interposed into the second signal path so that a bias current flows between the first amplifier stage and the interface circuit via the second amplifier stage, whereas the second signal path conveys the radio frequency signal.
A further aspect of the invention relates to an apparatus for amplifying an electrical signal. The apparatus comprises means for amplifying the electrical signal, and means for interfacing. The amplifying means comprise a first and a second means for amplifying the electrical signal. The first and second amplifying means are in communication via a first signal path and a second signal path. The means for interfacing are interposed into the second signal path so that a bias current flows between the first amplifying means and the interfacing means via the second amplifying means, whereas the second signal path conveys the radio frequen
Conexant Systems Inc.
Knobbe Martens Olson & Bear LLP
Vo Nguyen T.
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