A gain adjustment structure based on cascode low noise amplifier

Abstract

The invention discloses a gain adjustment structure based on a common gate cascode low noise amplifier. The gain adjustment structure comprises a coarse adjustment mode and a fine adjustment mode, the coarse adjustment mode reduces equivalent load impedance seen from a cascode tube NM2 source by the manner of connecting an additional load resistor in parallel while reducing cascode tube NM2 transconductance so as to adjust the gain, and the fine adjustment mode, reduces the equivalent load impedance seen from the cascode tube NM2 source by the manner of connecting the additional load resistor in parallel so as to adjust the gain. According to the gain adjustment structure disclosed by the invention, the fine adjustment mode is adopted, coupling capacitance is used, and a virtual ground is constructed, so that the adjustment range is larger; and in addition, due to the action of a power supply DC blocking capacitor, nearly no DC flows by a fine adjustment branch, and meanwhile a part of current in the original cascode tube is extracted for use in the coarse adjustment mode, and no additional power consumption is increased by the two adjustment methods.

Description

technical field [0001] The invention relates to a gain adjustment structure based on a common grid cascode low noise amplifier, which belongs to the low noise amplifier technology. Background technique [0002] The gain control mechanism is widely used in modern communication systems. Through gain control, the circuit can expand the dynamic range of the received signal, reduce power consumption and improve linearity. Especially in recent years, the rapid development of the portable RF terminal market has made power consumption an increasingly important consideration. The existence of signal attenuation and reflection causes the change of the signal power at the front end of the receiver, and the range of the input signal of the receiver can reach more than 80dB, such as from a small signal of a few microvolts to a large signal of tens of millivolts, low noise As the first stage circuit of the radio frequency receiving system, the amplifier LNA should have the ability to acc...

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Problems solved by technology

The switching path will cause loss, but as long as the loss is in an acceptable range, this technique is still feasible, and the gain and linearity are really uncontrollable

3. Changing the bias: This method is essentially to control the transconductance of the input tube, or to control the transconductance of the amplifier tube. It is easy to implement, and the gain flatness will not deteriorate when the gain changes, but the noise performance will deteriorate, and it is difficult to control accurately

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