Power consumption control for low noise amplifier

[0002] (1) Field of the Invention

[0003] This invention relates to low noise amplifier for wireless communication, in particular to the power consumption of the amplifier.

[0004] (2) Description of the Related Art

[0005] In mobile wireless communication system, power consumption is an important consideration. The low noise amplifier (LNA) is a major source of power gouging. It is desirable to operate the LNA at low current to conserve power. However, in the presence of jamming the LNA must have a large dynamic range and low intermodulation distortion. To meet these requirements, the LNA must operate at a high enough dc operating current. Thus, the design is often a balance between dynamic range and power consumption.

[0006] In a paper by Wei Xiong and Lawrence E. Larson “An S-band Low Noise Amplifier with Self-Adjusting Bias for Improved Power Consumption and Dynamic Range in a Mobile Environment”, IEEE Radio Frequency Integrated Circuits Symposium, 1999, it was disclosed to use a power detector to actively control the drain-source current of two cascaded GaAs FET amplifier of the LNA. The control circuit uses an average detector to detect the power level with respect to a fixed reference level. Such a detector detects the average magnitude of the jamming signal rather then the peak value of the jamming signal, whereas the LNA should be designed to accommodate the peak jamming signal rather than the average jamming signal. The fixed reference level may cause the LNA to operate at high current level in the presence of high desired signal. Furthermore, the Wei-Larson circuit was not integrated and there was significant parasitic element losses through the package device lead frame, printed circuit board traces, especially at high frequencies. Their diode and resistors are dissipative elements, as are the resistance voltage divider to derive the reference voltage. Therefore the prior art leaves something to be desired.

[0007] An object of this invention is to conserve the power consumption of a low noise amplifier for mobile communication system. Another object of this invention is to provide a control circuit to increase the operating current of the LNA in the presence of a jamming signal. Still another object of this invention is to detect the peak value of a jamming signal relative to the average signal level to control the power consumption of a LNA. A further object of this invention is to design a control circuit which can be integrated with MOSFET technology.

[0008] These objects are achieved by comparing the peak jamming signal with the average signal of input signal. The average signal is obtained by filtering the input signal with a low pass filter. The difference signal between the average input signal and the jammed input signal is detected by a peak detector. The detected signal is then again compared with the average input signal to obtain a dc control signal to control the power consumption of a LNA.

[0009] FIG. 1 shows a block diagram of this invention.

[0010] FIG. 2 shows the implementation of the control circuit with field effect transistors (FETs).

[0011] The block diagram of this invention is shown in FIG. 1. The input signal Vin is fed to one input of a differential peak detector 10 and fed through a low-pass filter LP1 to develop an average input signal Viav for inputting to another input of the differential peak detector 10. The differential peak detector 10 develops a rectified peak jamming signal at node Ns. The signal at node Ns is filtered again by a low pass filter LP2 to obtain an average dc jamming voltage proportional to the excess jam signal at node Nc. The voltage at node Nc is compared with the average input signal Viav in a differential amplifier 11. The dc output Vno1 and Vno2 of the differential amplifier 11 is a measure of the jamming signal in excess of the average input voltage and is used to control the dc current of the LNA (not shown).

[0012] FIG. 2 shows the implementation of FIG. 1 with field effect transistors (FET). The differential peak detector has a differential pair of n-channel MOSFETs Mni1 and Mni2. The input of Mni1 is directly fed from the input voltage V1 and the input of Mni2 is fed from Viav which is the average V1 filtered by a low pass filter RiCi. The differential pair is fed from the sources of n-channel MOSFETs Mni1 and Mni2 by a dc current source is comprising a current mirror n-channel MOSFET Mnb2 which mirrors the dc current Idc of n-channel MOSFET Mnb1. Normally without jamming signal, the current source Is is very low in the microampere range. The dc drain current of Mni1 is mirrored by the current mirror p-channel MOSFETs Mp1 and Mp2 such that the dc drain current of Mni1, Mp1, and Mp2 are equal and equal to one half that of Mn2. When there is a jamming signal applied to the gate of Mni1, the drain and source current increases for positive signal but is equal to zero at negative signal. The increased source current charges the peak detector capacitor C11 to develop a rectified voltage across C11 at node Ns. The rectified voltage at node Ns is filtered by Rf and Cf to develop a dc voltage Vf at node Nc. Meanwhile the average input voltage Viav is level shifted by the n-channel MOSFET Mnb3 to develop a reference voltage Vref. The level shifter Mni3 is sourced from another n-channel MOSFET current mirror Mnb3 which mirrors the current Is, and is drained by another p-channel MOSFET current mirror Mp4 and Mp5, which reduces the dc current through Mni3 to one half that of Mnb3. The dc detected peak jamming voltage at Nc is compared with the Vref in the differential amplifier comprising n-channel MOSFETs Mno1, Mno2 and current source Mnb4. Then the difference output current is a measure of the peak jamming signal with reference to the average input signal, and is used to control the dc operating current of the LNA during jamming period.

[0013] While preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in this art that various modifications may be made in these embodiments without departing from the spirit of the present invention. Such modifications are all within the scope of this invention.