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jiangwp
Joined: 27 Jul 2004
Posts: 184
Helped: 9
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 10 Jan 2005 12:11 How to determine the bandwidth of OP when designing a DAC |
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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 ?
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wee_liang
Joined: 04 Jan 2005
Posts: 26
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| 11 Jan 2005 2:21 Re: How to determine the bandwidth of OP when designing a DA |
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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
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nickooeda
Joined: 15 Sep 2004
Posts: 44
Helped: 2
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| 13 Jan 2005 6:02 How to determine the bandwidth of OP when designing a DAC |
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| u must recognize your singal bandwidth,and then decide the bandwidth of OP amp
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jordan76
Joined: 25 Mar 2004
Posts: 177
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| 13 Jan 2005 7:21 Re: How to determine the bandwidth of OP when designing a DA |
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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
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