SLOS712I – JANUARY 2011 – REVISED OCTOBER 2016
8.4 Device Functional Modes
8.4.1 Split-Supply Operation (±1.25 V to ±2.75 V)
To facilitate testing with common lab equipment, the OPA836 EVM (see OPA835DBV, OPA836DBV EVM,
SLOU314) is built to allow for split-supply operation. This configuration eases lab testing because the mid-point
between the power rails is ground, and most signal generators, network analyzers, oscilloscopes, spectrum
analyzers and other lab equipment have inputs and outputs with a ground reference.
Figure 58 shows a simple noninverting configuration analogous to Figure 53 with ±2.5-V supply and VREF equal
to ground. The input and output will swing symmetrically around ground. For ease of use, split supplies are
preferred in systems where signals swing around ground.
Figure 58. Split-Supply Operation
8.4.2 Single-Supply Operation (2.5 V to 5.5 V)
Often, newer systems use a single power supply to improve efficiency and reduce the cost of the power supply.
The OPA836 and OPA2836 devices are designed for use with a single supply with no change in performance
compared to a split supply, as long as the input and output are biased within the linear operation of the device.
To change the circuit from split supply to single supply, level shift of all voltages by half the difference between
the power supply rails. For example, changing from ±2.5-V split supply to 5-V single supply is shown in
Figure 59. Single-Supply Concept
A practical circuit will have an amplifier or other circuit providing the bias voltage for the input, and the output of
this amplifier stage provides the bias for the next stage.
Figure 60 shows a typical noninverting amplifiercircuit. With 5-V single-supply, a mid-supply reference generator
is needed to bias the negative side through RG. To cancel the voltage offset that would otherwise be caused by
the input bias currents, R1 is selected to be equal to RF in parallel with RG. For example, if gain of 2 is required
and RF = 1 kΩ, select RG = 1 kΩ to set the gain and R1 = 499 Ω for bias-current cancellation. The value for C
depends on the reference; TI recommends a value of at least 0.1 µF to limit noise.
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