[SOLVED] How to determine the bandwidth of OP when designing a DAC

[jiangwp]

When the rate of a DAC conversion is comfirm , it is how to determine the bandwith and slew rate of the OPAMP used as buffer .

Generally, we can assume single pole of OPAMP for simplification.
what is the relation format between the settling time constant and the bandwidth ?

 

[wee_liang]

Re: How to determine the bandwidth of OP when designing a DA

For single time constant unity-gain opamps, the output rises for a unit step input at the rate of

Vo = Vi (1-exp(-t/RC))

τ=RC=1/ωu

ωu is your unity gain bandwidth of the opamp

 

[nickooeda]

u must recognize your singal bandwidth,and then decide the bandwidth of OP amp

 

[jordan76]

Re: How to determine the bandwidth of OP when designing a DA

The settling time consists of two parts:linear and nonlinear settling segments.
For the linear part(due to the finite unit-gain frequency of the opamp), the time constant of the closed-loop opamp can be given:τ=1/ω, where ω is the unit-gain frequency of the opamp. As a rule of thumb, settling within 0.1 percent need about 7τ.
The nonlinear part is due to slew-rate limiting,thus strongly dependent on the output's step size. If the slew rate of the opamp is larger than (Vstep/τ),the nonlinear settling time will be zero.

Hope it helps!

regards,
jordan76