Variable gain amplifier for low voltage applications

An integrated receiver system comprising:

• a substrate;
• a receiver disposed on the substrate for converting a received signal to an IF signal;
• a VGA for low voltage applications coupled to the receiver for processing the IF signal, the VGA including a bank pair having a first bank of differential pairs of transistors and a second bank of differential pairs of transistors, the bank pair being cross-coupled in parallel, the IF signal being applied to the bank pair decoupled from a control signal used to control transconductance output gain of the bank pair over a range of input voltages;
• and
• a digital IF demodulator disposed on the substrate for converting the IF signal processed by the VGA for low voltage applications to a demodulated baseband signal.

A method for providing linear transconductance output gain of a bank pair over a range of differential input voltages, the bank pair having a first bank of differential pairs of transistors and a second bank of differential pairs of transistors, the bank pair being cross-coupled in parallel, each bank pair having a plurality of differential pairs of transistors, each differential pair of transistors having a first transistor, each first transistor having a first transistor drain coupled to a first differential pair output, a second transistor, each second transistor having a second transistor drain coupled to a second differential pair output, each first transistor having a first transistor source and each second transistor having a second transistor source, the first transistor source and the second transistor source being coupled to a respective current source for each differential pair of transistors, comprising:

• coupling a second transistor gate of each of the second transistors of the first bank to a respective first transistor gate of each of the first transistors of the second bank;
• applying a first differential input voltage to first transistor gates of each first transistor of the first bank;
• applying a second differential input voltage to second transistor gates of each second transistor of the second bank;
• applying a differential reference voltage across a resistive ladder coupled between the respective second transistor gates of the first and the respective first transistor gates of the second bank;
• and
• varying the current through the resistive ladder to control transconductance output gain of the bank pair over the range of input voltages.

A method for providing linear transconductance output gain over a range of differential input voltages for a first bank pair and a second bank pair of differential pairs of transistors cross-coupled in parallel, each bank pair having a plurality of differential pairs of transistors, each differential pair of transistors having a first transistor, each first transistor having a first transistor drain coupled to a first differential pair output, a second transistor, each second transistor having a second transistor drain coupled to a second differential pair output, each first transistor having a first transistor source and each second transistor having a second transistor source, the first transistor source and the second transistor source being coupled to a respective current source for each differential pair of transistors, comprising:

• coupling a second transistor gate of each of the second transistors of the first bank pair to a respective first transistor gate of each of the first transistors of the second bank pair;
• applying a first differential input voltage to first transistor gates of each first transistor of the first bank of the bank pair;
• applying a second differential input voltage to second transistor gates of each second transistor of the second bank of the bank pair;
• applying a differential reference voltage across a resistive ladder coupled between the respective second transistor gates of the first bank pair and the respective first transistor gates of the second bank pair;
• and
• increasing the current through the resistive ladder to lower transconductance output gain while expanding the range of input voltages.