US 8,258,869 B2 · Low noise amplifier with current bleeding branch

Abstract

An LNA circuit for providing a wide range of gain while maintaining the output headroom. In a radio frequency (RF) receiver, the signal received by the receiver may be extremely small. For a transmitter in a short distance, the received signal may be relatively strong. A low power amplifier usually is used to amplify the input signal. The LNA has to be designed to accommodate a wide range of gain. A convention LNA circuit supporting a wide range of gain often suffers from reduced output headroom due to increased current through the load resistor. The present invention discloses the use of current bleeding branch to allow a portion of current to flow through the current bleeding branch and consequently reduces the current that would have flown through the load resistor. Consequently, the voltage across the load resistor may be maintained low to allow adequate output headroom.

Claims10

Dependent claims

A low-noise amplifier comprising:

an input transconductance stage that receives an input voltage signal;
a cascode transistor pair that is coupled to the input transconductance stage to generate an amplified output signal;
and
an output load stage coupled to the amplified output signal, wherein the output load stage comprises a first load resistor coupled to an adjustable current source branch in parallel;
and
wherein the output load stage further comprises a switchable branch coupled to the first load resistor and the adjustable current source branch in parallel, wherein the switchable branch comprises a second load resistor connected to a load switch in serial to select a gain mode.

3 more elements

Dependencies are inferred from the claim text.

Low noise amplifier with current bleeding branch

Life of this patent

Low noise amplifier with current bleeding branch

Life of this patent

Abstract

Claims10