Scaling a signal.

[jgalak]

I need to rescale an input signal.  The source signal is a sine wave with amplitude of about 5 Vpp and a DC offset of 2.5V.  In other words, it swings between ground and +5V, centered on 2.5V.  I need it to swing between ground and 3.3V, centered on 1.65V.  The frequency is in the range of about 1 - 2.5kHz.

My first attempt was to use a fractional gain non-inverting opamp amplifier, but that got me a 3.3Vpp signal centered on 2.5V, swinging between .85V and 4.15V (appreciate ox numbers).

One idea I had was to AC couple the output of the amp, and then rebias it to the correct offset voltage, using a circuit like the one attached (copied from Learning the Art of Electronics), using the appropriate  ratio resistors between 5v and ground.

Is there a better way to accomplish this?  Maybe with a single step of attenuation and rebiasing?

[hexreader]

Won't a simple resistor voltage divider do that job?

Something like 1k7 Ohms and 3k3 Ohms.

Sounds too simple, so maybe I am missing the point?

[jgalak]

You mean both attenuate and change the offset?  Hmm, yeah, that should work.  Almost seems to easy...

Especially if I throw a buffer Op-Amp on our or both sides of the divider, to help with loading.  The source of the signal is an R2R ladder, so I'd be concerned that without a buffer between it and the divider it would get distorted by the loading. 

Not sure if I need a second buffer at the other end, the signal is going to be a control signal to an IC, but the data sheet doesn't list input impedance for that pin, just that it's a max current of 20 uA.

[David Hess]

All that is required in this case is a resistor divider with a ratio of 3.3/5.0 so 0.660.  A voltage follower could be used at the output to buffer the attenuator.