Patent ID: 7443241

Claim:
A RF variable gain amplifier circuit for enabling linear control of an output gain current, comprising: a linear voltage-to-current converter for transforming a control voltage linearly into a decibel current, wherein the decibel current is linearly proportional to the control voltage; a current-control circuit for splitting the decibel current into a first control current and a second control current, wherein the decibel current equals to a difference between the first control current and second control current; a first amplifier for receiving the first control current and for receiving a first input voltage, the first amplifier being capable of transforming the first input voltage into a first output current according to the difference; and a second amplifier for receiving the second control current and for receiving a second input voltage, the second amplifier being capable of transforming the second input voltages into a second output current according to the difference, wherein the difference between the first and the second output currents is proportional to the output gain current, wherein the first amplifier further comprising a first gain transistor having a gate end, a first end, and a second end, the first gain transistor being capable of receiving the first input voltage, wherein the first control current being capable of passing from the second end of the first gain transistor to the first end of the first gain transistor, and a first cascode transistor having a drain end and a first end; the first cascode transistor being capable of outputting the first output current, wherein the first end of the first cascode transistor being connected to the second end of the first gain transistor, wherein the second amplifier further comprising a second gain transistor having a gate end, a first end, and a second end, the second gain transistor being capable of receiving the second input voltage, wherein the second control current being capable of passing from the second end of the second gain transistor to the first end of the second gain transistor, and a second cascode transistor having a drain end and a first end; the second cascode transistor being capable of outputting the second output current, wherein the first end of the second cascode transistor being connected to the second end of the second gain transistor.