Design Goals

Design Description

This circuit converts a single ended input of 0.1V to 2.4V into a differential output of ±2.3V on a single 2.7V supply. The input and output ranges can be scaled as necessary as long as the op amp input common-mode range and output swing limits are met.

Design Notes

1. Op amps with rail-to-rail input and output maximizes the input and output range of the circuit.
2. Op amps with low V_os and offset drift reduces DC errors.
3. Use low tolerance resistors to minimize gain error.
4. Set output range based on linear output swing (see A_ol specification).
5. Keep feedback resistors low or add capacitor in parallel with R₂ for stability.

Design Steps

1. Buffer V_i signal to generate V_o+.
   ${\mathrm{V}}_{\mathrm{O}+}={\mathrm{V}}_{\mathrm{i}}$
2. Invert and level shift V_o+ using a difference amplifier to create V_o–.
   ${\mathrm{V}}_{\mathrm{o}-}=\left({\mathrm{V}}_{\mathrm{ref}}-{\mathrm{V}}_{\mathrm{o}+}\right)\times \left(\frac{{\mathrm{R}}_2}{{\mathrm{R}}_1}\right)$
3. Select resistances so that the resistor noise is smaller than the amplifier broadband noise.
   ${\mathrm{E}}_{\mathrm{nv}}=30\mathrm{}\frac{\mathrm{nV}}{\sqrt{\mathrm{Hz}}}\text{ (Voltage noise from op amp)}$
   $\text{If }{\mathrm{R}}_1={\mathrm{R}}_2={\mathrm{R}}_3={\mathrm{R}}_4=49.9\mathrm{k\Omega }\text{ then}$
   ${\mathrm{E}}_{\mathrm{nr}}=\sqrt{{\left(\sqrt{4\times \mathrm{kB}\times \mathrm{T}\times \left[{\mathrm{R}}_1\right|\left|{\mathrm{R}}_2\right]}\right)}^2+{\left(\sqrt{4\times \mathrm{kB}\times \mathrm{T}\times \left[{\mathrm{R}}_3\right|\left|{\mathrm{R}}_4\right]}\right)}^2}=28.7\frac{\mathrm{nV}}{\sqrt{\mathrm{Hz}}}{\text{ (<E}}_{\text{nv}}\text{)}$
4. Select resistances that protect the input of the amplifier and prevents floating inputs. To simplify the bill of materials (BOM), select R₅ = R₆.
   ${\mathrm{R}}_5={\mathrm{R}}_6=49.9\mathrm{k\Omega }$

Design Simulations

DC Simulation Results

AC Simulation Results

Design References

Texas Instruments, Simulation for Single-Ended Input to Differential Output, circuit SPICE simulation file

Texas Instruments, Single-Ended Input to Differential Output Conversion Circuit, reference design

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