Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
1998-12-22
2002-03-05
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S282000, C330S129000, C455S241100
Reexamination Certificate
active
06353364
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to digitally gain controllable amplifiers, and more particularly, a digitally gain controllable amplifier controllable by an analog gain control signal, and having an on-chip decoder and programmable gain distribution.
BACKGROUND OF THE INVENTION
In a typical “homodyne” receiver, a variable gain amplifier (VGA) may be used to maintain a constant signal amplitude to a load independent of the input signal amplitude. This variable gain amplifier may be implemented with either an analog variable gain amplifier, or a digital variable gain amplifier.
Using an analog variable gain amplifier has many disadvantages such as the requirement of complicated circuitry for maintaining a linear-in-dB gain control characteristic, as well as large chip area requirements for the temperature compensation and predistortion circuit that is used to control the analog variable gain amplifier. Furthermore, the predistortion and temperature compensation circuits consume a significant amount of supply current. Additionally, the analog gain controlled VGAs are noisy as the signal-to-noise ratio at the output of the amplifier depends on the gain setting. Further, analog gain controlled amplifiers essentially constitute amplitude modulators as the gain of the variable gain amplifier could vary as the instantaneous noise voltage overlaying the voltage control signal varies.
Because the digital gain controlled VGAs overcome many of the disadvantages of the analog gain controlled VGAs, it is desirable to use digital gain controlled VGAs. However, digital gain controlled VGAs have one major disadvantage: a required isolation of greater than 60 dB between the serial digital gain control word inputs and the RF signal input of the digital gain controlled VGA, in order to keep a spur generated at the signal frequency at the same level as the noise floor. This attenuation requirement is difficult to achieve when taking into account the parasitic effects that occur within the chip's package and on the board that the chip is attached to.
Additionally, in a digital gain controlled VGA, the digital gain control word sent to the digital VGA must be in a specific format for use by the amplifiers present in the digital VGA. This generally requires that the digital gain controlled VGA be used only in conjunction with specific supporting external circuitry.
Further, while designing a radio receiver utilizing a typical digital gain controlled VGA having multiple amplifying circuits, the operating conditions for the receiver must be predicted in advance in order to set the gain distribution of the multiple amplifier circuits to achieve optimal noise and linearity performance. However, because the operating conditions for the radio receiver are constantly changing, this gain distribution does not yield optimal noise and distortion performance for the majority of the time that the receiver is operating.
The present invention is directed to overcoming one or more of the problems discussed above in a novel and simple manner.
SUMMARY OF THE INVENTION
In accordance with the invention, there is disclosed a digitally gain controllable amplifier controllable by an analog gain control signal. There is further disclosed a digitally gain controllable amplifier having an on-chip decoder. Additionally, there is disclosed a digitally gain controllable amplifier having a programmable gain distribution.
It is an object of the invention to provide a method of controlling a digital variable gain amplifier (DVGA) of a receiver where the DVGA includes an amplifier circuit, the method including the steps of receiving an analog gain control signal indicating a desired gain for the DVGA, and converting the analog gain control signal to a digital gain control signal. The method further includes applying the digital gain control signal to the amplifier circuit to achieve the desired gain, where the amplifier circuit has a gain controlled by the digital gain control signal.
It is a feature of the invention that the DVGA includes a plurality of amplifier circuits, and the method includes decoding the digital gain control signal into a plurality of gain settings, where each gain setting corresponds to one of the plurality of amplifier circuits. The method then includes applying each gain setting to a corresponding amplifier circuit in the DVGA to achieve the desired gain. It is an additional feature of the invention that the digital gain control signal is a final digital gain control signal and an initial digital gain control signal is determined by gain control circuitry, and the initial digital gain control signal is converted to the analog gain control signal. In a further preferred embodiment, the DVGA includes a plurality of amplifier circuits and the method includes controlling the noise and linearity characteristics of the DVGA by changing the distribution of gain across the plurality of amplifier circuits.
It is another object of the invention to provide a method of controlling a DVGA where the DVGA has a plurality of amplifier circuits and the gain of each amplifier circuit is controlled by a gain setting, the method including determining the desired noise and linearity characteristics of the DVGA for a time period. The method also includes increasing the gain setting of a first amplifier circuit, while decreasing gain settings for at least one of a remainder of the plurality of amplifier circuits in the DVGA if an improved/increased noise characteristic is desired for the time period. The method further includes decreasing the gain setting of the first amplifier circuit, while increasing the gain settings for at least one of the remainder of the plurality of amplifier circuits in the DVGA if an increased linearity characteristic is desired for the time period.
It is a feature of the invention that a received signal strength (RSS) is determined for a received signal where the desired noise and linearity characteristic is set for decreased noise if the RSS does not exceed an RSS threshold, and the desired noise and linearity characteristic is set for increased linearity if the RSS exceeds the RSS threshold. It is an additional feature of the invention that the bit error rate (BER) of a detected signal may be used in addition to the RSS where the determined noise and linearity characteristics are maintained if the BER does not exceed a BER threshold, and if the BER exceeds the BER threshold, the desired noise and linearity characteristics are set according to the RSS. It is an additional feature of the invention that an analog gain control signal is received indicating a desired gain for the DVGA, and the analog gain control signal is converted to a digital gain control signal. In a further feature of the invention, a gain control signal is received and encoded into a plurality of gain settings where each gain setting corresponds to one of the plurality of amplifier circuits.
It is an object of the invention to provide a DVGA where the DVGA has an amplifier circuit controlled by a digital gain control signal, the DVGA applying a desired gain to a received signal from a signal source and applying the amplified received signal to the load. The DVGA also includes an analog-to-digital (A/D) converter coupled to the amplifier circuit for receiving an analog gain control signal and converting the analog gain control signal to the digital gain control signal and applying the digital gain control signal to the amplifier circuit.
It is a feature of the invention wherein the DVGA comprises a plurality of amplifier circuits, and further comprises a decoder connected between the A/D converter and the plurality of amplifier circuits for decoding the digital gain control signal into a plurality of gain settings, where each gain setting corresponds to one of the plurality of amplifier circuits. It is another feature of the invention where the digital gain control signal is a final digital gain control signal and a digital-to-analog (D/A) converter external to the DVGA and coupled to the A/D converter receives a
Coats & Bennett P.L.L.C.
Ericsson Inc.
Nguyen Khanh Van
Pascal Robert
LandOfFree
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