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Hi all: I am designing a GainBoosted OPA, now there have some questions that needed to be resolved!
The load of the OPA is 1.5pF, and the GBW of the OPA is 300MHz.
At first, I design the MAIN OPA of the GainBoosted OPA and the GBW of the MAIN OPA is 300MHz, the load of the OPA is 1.5pF, the phase margin of the MAIN OPA is 53.
After designing the MAIN OPA, I design Nmos_INPUT AUXILIARY OPA and Pmos_INPUT AUXILIARY OPA. The GBW of the Nmos_INPUT AUXILIARY OPA is 373MHz, the load of the OPA is 0.6pF, the phase margin of the MAIN OPA is 84; The GBW of the Pmos_INPUT AUXILIARY OPA is 381MHz, the load of the OPA is 0.6pF, the phase margin of the MAIN OPA is 84.
But after the simulation, I found that the The GBW of the GainBoosted OPA is 336MHz, the phase margin of the GainBoosted OPA is only 20(the load of the OPA is 1.5pF).
I think the pole and the zero shoul be at the unity-gain frequency, so if the phase margin of the MAIN OPA is 53, the phase margin of the GainBoosted OPA should be 53, I do not know why the phase margin of the GainBoosted OPA is only 20?
Help me, please. thanx!!
The full schematic and the netlist of the OPA can be found at the attachment: the gain_boosted.pdf is the MAIN OPA; the auxiliary_n.pdf is the Nmos_INPUT AUXILIARY OPA; the auxiliary_p.pdf is the Pmos_INPUT AUXILIARY OPA; cmfb_n.pdf is the CMFB circuit of the Nmos_INPUT AUXILIARY OPA; cmfb_p.pdf is the CMFB circuit of the Pmos_INPUT AUXILIARY OPA; the opa_bias_improve.pdf is the BIAS circuit of the GainBoosted OPA and the AUXILIARY OPA; balun.pdf can be used to AC simulation; the Gain_Boosted_ac.sp is the netlist of the OPA, and the csmc.lib is the library file of the OPA.
The load of the OPA is 1.5pF, and the GBW of the OPA is 300MHz.
At first, I design the MAIN OPA of the GainBoosted OPA and the GBW of the MAIN OPA is 300MHz, the load of the OPA is 1.5pF, the phase margin of the MAIN OPA is 53.
After designing the MAIN OPA, I design Nmos_INPUT AUXILIARY OPA and Pmos_INPUT AUXILIARY OPA. The GBW of the Nmos_INPUT AUXILIARY OPA is 373MHz, the load of the OPA is 0.6pF, the phase margin of the MAIN OPA is 84; The GBW of the Pmos_INPUT AUXILIARY OPA is 381MHz, the load of the OPA is 0.6pF, the phase margin of the MAIN OPA is 84.
But after the simulation, I found that the The GBW of the GainBoosted OPA is 336MHz, the phase margin of the GainBoosted OPA is only 20(the load of the OPA is 1.5pF).
I think the pole and the zero shoul be at the unity-gain frequency, so if the phase margin of the MAIN OPA is 53, the phase margin of the GainBoosted OPA should be 53, I do not know why the phase margin of the GainBoosted OPA is only 20?
Help me, please. thanx!!
The full schematic and the netlist of the OPA can be found at the attachment: the gain_boosted.pdf is the MAIN OPA; the auxiliary_n.pdf is the Nmos_INPUT AUXILIARY OPA; the auxiliary_p.pdf is the Pmos_INPUT AUXILIARY OPA; cmfb_n.pdf is the CMFB circuit of the Nmos_INPUT AUXILIARY OPA; cmfb_p.pdf is the CMFB circuit of the Pmos_INPUT AUXILIARY OPA; the opa_bias_improve.pdf is the BIAS circuit of the GainBoosted OPA and the AUXILIARY OPA; balun.pdf can be used to AC simulation; the Gain_Boosted_ac.sp is the netlist of the OPA, and the csmc.lib is the library file of the OPA.