Programmable Gain Amplifier (PGA) Basics and Types

This page covers Programmable Gain Amplifier (PGA) basics and mentions Programmable Gain Amplifier (PGA) types. The device which amplifies the input signal is known as an amplifier.

The device by which variable gain can be obtained is known as a programmable gain amplifier. It is also known by its abbreviation as PGA.

Figure 1 depicts simple PGA inputs and outputs. As shown, PGA needs programmable inputs (A0, A1) and supply voltages (V+, V-) for its operation. Usually, CMOS or TTL compliant inputs are used as programmable inputs.

The gain in the order of 1, 10, and 100 can be achieved using a typical PGA. Sometimes, three pins are also used as programmable inputs.

The Programmable Gain Amplifier is used in systems that require a wider dynamic range. The common applications of PGA include data acquisition systems, medical instrumentation, and general-purpose analog boards, etc. The major vendors of PGA include Analog Devices Inc., Texas Instruments Incorporated, etc.

Programmable Gain Amplifier (PGA) Types | Difference between Resistive PGA and Capacitive PGA

There are two types of programmable gain amplifiers (PGAs): resistive PGA and capacitive PGA. Resistive PGA uses resistors, while capacitive PGA uses capacitors at the inputs of the Operational Amplifier ICs used in the design.

The following points compare resistive PGA vs. capacitive PGA and mention the difference between resistive PGA and capacitive PGA. These are the advantages of capacitive PGA over resistive PGA.

• It consists of fewer noise sources, and fewer amplifiers are required.
• Capacitors do not contribute to noise generation, while resistors do contribute to noise generation.
• Capacitors do not suffer from the problem of self-heating, unlike resistors. Moreover, they offer better matching as well as stability against temperature drift. Due to this, capacitive PGA results in positive results in terms of gain error, offset, and drift specifications.
• The capacitors are components that de-couple the input common mode from the rest of the signal chain common modes. This will offer benefits in CMRR, THD, and PSRR specifications as desired in the PGA devices.