Texas Instruments’ PGA20 x series

One, Two, Gain!

Test equipment and sensors both profit from amplifiers which change their gain on the fly. One of Texas Instruments evergreens recently saw quite a bit of additional attention.

From a technical point of view, the part is extremely simple. As shown in the figure, the part – in essence – is an operational amplifier which subtracts the two inputs and emits the result after multiplying it with a specified gain factor. The really interesting aspect is the set of digital inputs which allow users to pick the wanted voltage level comfortably.

PGA20 x parts are easy to use

Texas Instruments provides two different part families, which differ by the gain levels implemented. Figure two shows the available amplifier levels – simply order the one ideally suited to your application.

Texas Instruments provide two amplification classes

Texas Instruments provide two amplification classes

While the parts power supply demands – it can work from a dual 6V supply but works best with +/-15V – are handle-able, be aware that the PGA family’s full gain bandwidth is limited to a few ten Kilohertz at best. This, clearly, is not a part intended to handle high-speed signals.

A question of performance

Being a development by Burr Brown, the PGA20 x family comes with a group of nifty tweaks not found in other opamp families. For example, output sensing is not done inside of the chip – instead, a dedicated pin lets you “slide in” amplifiers as shown in figure three.

The power booster’s gain error is eliminated via the feedback circuit

The power booster’s gain error is eliminated via the feedback circuit

The part can even be cascaded in a “family group”. If one PGA20 2 and one PGA20 3 are ganged up, the amount of selectable amplification levels increases greatly.

Conclusion

While the PGA20 2 / PGA20 3 family definitely is not the newest part on the market, it is a well-proven design which saw use in more than one piece of high-value test equipment. If your circuit can live with the relatively moderate speed and the large DIP housing, definitely to give the part a chance!

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