Programmable Gain Amplifier (PGA)

This document shows two circuits that use a precise, negative temperature coefficient (NTC) thermistor for temperature measurement. The thermistor is placed in a resistive divider to linearize the voltage response to temperature. This voltage is then processed in the analog domain, by the MCP6S2X Programmable Gain Amplifier (PGA), before converting to digital. The first circuit uses a more precise analog-to-digital converter (ADC), while the second circuit employs a less precise ADC. The design tradeoffs between these approaches will be discussed. These circuits take advantage of the MCP6S2X's input MUX, which have 1, 2, 6 or 8 inputs. This PGA is used to process multiple signals and/or temperatures, and digitally set the most appropriate gain for each input. This reduces overall design complexity and allows for the temperature correction of other sensors.

Photo sensors bridge the gap between light and electronics. Microchip’s Programmable Gain Amplifiers (PGAs) are not well suited for precision applications (such as CT scanners), but they can be effectively used in position photo sensing applications minus the headaches of amplifier stability. When the two, six or eightchannel PGA is used in this system, the other channels can be used for other sensors or an array of photo sensors without an increase in signal conditioning hardware or PICmicro® microcontroller I/O pin consumption. The multiplexer and high-speed conversion response of the PGA / ADC conversion allows the photo sensor input signal to be sampled and quickly converted to the digital domain. Switching from channel-to-channel is then easier with the Serial Peripheral Interface (SPI™) from the PICmicro microcontroller to the PGA.

This document shows how to select a temperature sensor and conditioning circuit to maximize the measurement accuracy and simplify the interface to the MCU. Practical circuits and interface techniques will be provided for embedded applications with thermocouples, Resistive Temperature Detectors (RTDs), thermistors and silicon integrated circuit temperature sensors. The attributes of each temperature sensor and the advantages of analog, ramp rate, frequency, duty cycle, serial and logic output solutions will be discussed. An analog output thermocouple circuit will be compared with a frequency output RTD oscillator circuit, along with design examples using serial and analog output silicon Integrated Circuit (IC) sensors. In addition, a Programmable Gain Amplifier (PGA) circuit will be shown that can increase the effectiveness of the analog-to-digital converter (ADC) bit resolution of a non-linear thermistor sensor.

Although it is simple to measure temperature in a stand-alone system without the help of Microchip's Programmable Gain Amplifiers (PGA), a variety of problems can be eliminated by implementing temperaturesensing capability in multiplexed applications with a PGA. One of the main advantages is that you can eliminate a second signal path to the microcontroller and still maintain the accuracy of your sensing system. In particular, the multiplexed PGAs you can use are the MCP6S22 (two-channel), MCP6S26 (six-channel), and MCP6S28 (eight-channel).

This document shows two circuits that use a precise, negative temperature coefficient (NTC) thermistor for temperature measurement. The thermistor is placed in a resistive divider to linearize the voltage response to temperature. This voltage is then processed in the analog domain, by the MCP6S2X Programmable Gain Amplifier (PGA), before converting to digital. The first circuit uses a more precise analog-to-digital converter, while the second circuit employs a less precise analog-to-digital converter. The design tradeoffs between these approaches will be discussed. These circuits take advantage of the MCP6S2X’s input MUX, which have 1, 2, 6 or 8 inputs. This programmable gain amplifier is used to process multiple signals and/or temperatures, and digitally set the most appropriate gain for each input. This reduces overall design complexity and allows for the temperature correction of other sensors.