Intermodulation distortion reduction circuit utilizing variable attenuation
First Claim
1. An intermodulation (IM) distortion reduction circuit for a radio frequency (RF) receiver having an RF input signal receiver line, said IM distortion reduction circuit comprising:
- a variable attenuator connected to attenuate and reduce IM distortion for RF signals on the RF input signal receiver line of the RF receiver; and
an attenuation controller coupled to said variable attenuator to control attenuation by said variable attenuator responsive to RF input signal power levels,wherein said attenuation controller includes an operational amplifier, wherein said operational amplifier includes an attenuator control input coupled to a received RF signal strength indication source, a threshold level input, and an amplified comparison output coupled to an input of said variable attenuator, andwherein said attenuator controller further includes an attenuator enabler coupled to said attenuator control input, wherein said attenuator enabler includes a switch with a control input, a ground input, and an enabling output coupled to said attenuator control input.
4 Assignments
0 Petitions
Accused Products
Abstract
A variable attenuator circuit provides variable attenuation responsive to received signal strength in a receiver to reduce intermodulation (IM) distortion. In a dual-mode frequency modulation/code division multiple access (FM/CDMA) cellular telephone implementation, the variable attenuator circuit decreases IM distortion by variably attenuating received radio frequency (RF) signals before an initial RF amplification stage to reduce the level of undesirable frequency mixing products. The variable attenuator circuit is turned on (activated) and off (deactivated) at a single, relatively low, input power level. An attenuator enable signal is also supplied from a logic unit of the mobile station to enable operation of the variable attenuator circuit throughout operation in a digital mode. Thus, while enabled, as soon as the input signal power level rises above a defined activation threshold amount, the variable attenuator circuit is activated and begins attenuating the input signal responsive to input signal power levels based upon a received signal strength indication output from a separate automatic gain control circuit. After the attenuation begins gradually, thus avoiding excessive chattering without the need for hysteresis, the attenuation rises non-linearly and continuously to quickly mitigate IM distortion problems.
-
Citations
23 Claims
-
1. An intermodulation (IM) distortion reduction circuit for a radio frequency (RF) receiver having an RF input signal receiver line, said IM distortion reduction circuit comprising:
-
a variable attenuator connected to attenuate and reduce IM distortion for RF signals on the RF input signal receiver line of the RF receiver; and an attenuation controller coupled to said variable attenuator to control attenuation by said variable attenuator responsive to RF input signal power levels, wherein said attenuation controller includes an operational amplifier, wherein said operational amplifier includes an attenuator control input coupled to a received RF signal strength indication source, a threshold level input, and an amplified comparison output coupled to an input of said variable attenuator, and wherein said attenuator controller further includes an attenuator enabler coupled to said attenuator control input, wherein said attenuator enabler includes a switch with a control input, a ground input, and an enabling output coupled to said attenuator control input. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
-
9. An RF input circuit for a radio frequency (RF) receiver, said RF input circuit comprising:
-
an RF antenna; a duplexer including an antenna input and an RF signal receiver output, wherein said antenna input is coupled to said RF antenna; an RF amplifier including an RF signal input and an RF signal output, wherein said RF signal input is coupled to said RF signal receiver output of said duplexer; a variable attenuator including an attenuator input coupled to both said RF signal receiver output of said duplexer and said RF signal input of said RF amplifier; and an attenuation controller coupled to said variable attenuator to control attenuation by said variable attenuator responsive to RF input signal power levels, wherein said attenuator controller further includes an attenuator enabler coupled to said attenuation controllers, and wherein said attenuator enabler includes a switch with a control input, a ground input, and an enabling output coupled to said attenuator control input. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
-
Specification