2.1.5 Programmable Gain Amplifier (PGA) with the TS4100

Analog signals can vary in amplitude and frequency especially when considering various taypes of sensors such as thermistors, strain

gauges, and photodiodes. To process the analog signals provided by the sensor, a stand-alone ADC such as a TS7001 or TS7003 can

be used. However, to take advantage of the resolution of the ADC, the analog signals must be scaled up to the maximum input voltage

range of the ADC.

One way to achieve this is by designing a 1.5 V non-inverting programmable gain amplifier (PGA) that incorporates a TS1005 opera-

tional amplifier and a TS4100 analog multiplexer as shown in the figure below. The gain can be changed from 2 to 8 via address pins

ADDA, ADDB, and ADDC.

With the TS4100 connected to ground, the on-resistance of the switch becomes part of the gain of the amplifier and needs to be ac-

counted for in the following gain equation: GAIN = 1 +

R1

RGX + RON

where RON is 80 Ω (typ) and RGX is the resistor connected to the TS4100 input. Unlike other analog switches, the TS4100 on-resist-

ance variation over the entire signal swing range is less than 1%. In this circuit, the corresponding gain variation is less than 0.03%

across all channels. This circuit accommodates an input signal bandwidth of 2.5 kHz to 10 kHz. Also, by connecting the TS4100 to

ground, internal switching spikes are minimized. Refer to 2.1.7 Charge Pump Effect Considerations.

Figure 2.1. Non-Inverting Programmable Gain Amplifier (PGA) with TS4100

TS4100/01/02 Data Sheet

System Overview

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