Programmable Gain Amplifier basics | PGA 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 amplifier. The device by which variable gain can be obtained is known as programmable gain amplifier. It is also known by its abbreviation as PGA.
The figure-1 depicts simple PGA inputs and outputs. As shown PGA need 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 1, 10 and 100 can be achieved using typical PGA. Sometimes three pins are also used as programmable inputs.
The Programmable Gain Amplifier is used in the systems which require 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) viz. 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.
Following points compare resistive PGA vs capacitive PGA and mentions difference between
resistive PGA and capacitive PGA. These are the advantages of capacitive PGA over resistive PGA.
• It consists of less noise sources and less number of amplifiers are required.
• Capacitors do not contribute in noise generation while resistors do contribute in noise generation.
• Capacitors do not suffer from problem of self heating unlike resistors. Moreover they offer better matching as well as stability against temperature drift. Due to this capacitive PGA results into positive results in terms of gain error, offset and drift specifications.
• The capacitors are components which de-couple input common mode from rest of signal chain common modes. This will offer benefits in CMRR, THD amd PSRR specifications as desired in the PGA devices.
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