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PSoC 5, 3 & 1

MaTr_1730276
New Contributor II

Hi everyone,

   

is there a way to modify a PGA component to allow GAIN < 1 ?

   

Kind regards

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1 Solution
DennisS_46
Employee

The PGA is made from an opamp, a resistor string, and a bunch of switches. In PSoC1, the top of the resistor string was switchable to the opamp output. Thus we could make a voltage follower followed by a resistive divider made from the tap. Cool, but it has its problems. The switch in series with the upper section of the tap can add as much as 0.7% non-linearity depending on absolute signal voltage and the 5.0 or 3.3 V power supply. This was a huge error for most customers, so in PSoC3, 5LP, and 4, the upper end of the tap is hard-wired to the opamp output. This gives better accuracy in PGA, but loses the divider that was often handy in PSoC1.

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2 Replies
odissey1
Honored Contributor II

Not really, you have to use external components

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DennisS_46
Employee

The PGA is made from an opamp, a resistor string, and a bunch of switches. In PSoC1, the top of the resistor string was switchable to the opamp output. Thus we could make a voltage follower followed by a resistive divider made from the tap. Cool, but it has its problems. The switch in series with the upper section of the tap can add as much as 0.7% non-linearity depending on absolute signal voltage and the 5.0 or 3.3 V power supply. This was a huge error for most customers, so in PSoC3, 5LP, and 4, the upper end of the tap is hard-wired to the opamp output. This gives better accuracy in PGA, but loses the divider that was often handy in PSoC1.

View solution in original post

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