What Is a Programmable-Gain Amplifier?
A programmable-gain amplifier is an amplifier that allows the user to change the magnitude of gain by programming.
It is an amplifier that uses operational amplifiers and generally has a non-inverting configuration. Because the gain can be adjusted through programming, programmable-gain amplifiers leave room for change in the signal chain, where analog signals are converted to digital signals.
This leads to the development of flexible products since it is possible to respond flexibly to customer or user wishes, such as increasing the signal reception strength, by changing the gain later.
Uses of Programmable-Gain Amplifiers
Programmable-gain amplifiers are mainly used for signal amplification in devices that receive signals or noise, such as communication equipment, detectors, and analyzers. Examples include base stations and receivers for cellular phones, ultrasonic radar, wireless communications, and voice analysis. Other applications include motor control.
When selecting specifications for programmable-gain amplifiers, the range and type of programmable gain, impedance magnitude, and gain accuracy should be considered.
Principle of Programmable-Gain Amplifiers
Programmable-gain amplifiers use a ladder configuration of resistors in the negative feedback circuit section of operational amplifiers and switch these resistor values via switch operation by controlling the register values of digital circuits. This enables gain switching and amplifier operation with a wide dynamic range.
In addition to the resistance value of the negative feedback circuit section, another technique is to change the internal voltage applied to the op amp by programming, which allows the amplification factor of the op amp itself to be varied to change the magnitude of gain. Programmable-gain amplifiers for equipment used in medical devices and scientific experiments require amplifiers with a large dynamic range, low noise, and excellent temperature stability.
For this reason, some products incorporate resistors or capacitors in the programmable-gain amplifiers to form a low-pass filter and eliminate high-frequency noise. Also available are products that connect multiple operational amplifiers with a circuit that has a programmable switch, etc., so that the operational amplifiers can be operated by the program as needed, enabling efficient and large amplification.
Other Information on Programmable-Gain Amplifiers
1. Programmable-Gain Amplifiers Used in Sensor Applications
In the design of a system using sensors, the output range of various types of sensors is designed to match the input range of the A-D converter in the subsequent stage, but the input-output range in the system does not always match. In such cases, programmable-gain amplifiers should be used between the sensor and the A-D converters to cover the sensor’s very low output range at very low levels and match the input range of the A-D converters.
In the case of sensor applications, noise levels must naturally be taken into account due to their application role. Instrumentation amplifiers are also often used, but programmable-gain amplifiers can be thought of as instrumentation amplifiers with an additional variable gain function in the second stage.
2. Difference Between Programmable-Gain Amplifiers (PGA) And Variable-Gain Amplifiers (VGA)
Both are the same in the sense that they are amplifiers whose gain can be changed and adjusted. Programmable-gain amplifiers (PGAs) are used for gain adjustment of discrete (precise) values because they are digitally controlled and bit-switched (4x, 8x, 16x, etc.) rather than continuously adjusted in an analog fashion.
Note that there is only as much adjustment resolution in the gain setting as the number of bits in the adjustment register. A variable gain amplifier (VGA), on the other hand, is an analog, continuous gain control with a relatively fast response and is suitable for applications that require AGC (automatic gain control) operation.