products:

Function:
Variable Gain Amplifiers (VGAs) are used to adjust the gain of an amplifier chain, often to prevent overdrive of components downstream from the VGA. VGAs are common in systems that need to handle a wide range of signal levels.

In linear systems, it can be important to preserve the output IP3 of the VGA as the gain varies. Systems using constant-envelope modulation techniques may be more concerned with a constant drive level out of the VGA, and may focus on limiting properties rather than distortion products.

One approach to creating variable gain is to cascade Gain Stages with Attenuators. The attenuators may be either PIN diode based, or Integrated Circuits.

Schematic symbol:

Key Specifications Gain Control Range Range: 10 to 70 dB per stage Limiting magnitude: tenths of dBs to dBs phase: tenths to 10s of degrees Output Intercept Point (IP3 out) Range: +15 to +40 dB Gain (G, S21) Range: 0 to 20 dB per stage

 

Discrete Devices:

PIN Diodes (for attenuators)

Integrated Circuits:

Variable Gain Amplifiers

IC Attenuators