what kind of circuit structure can I use to obtain high output impedance?
The biasing of a cascode is very simple ! You just apply a DC voltage to the gate of the cascoded transistor. Note that in your picture this is also the case although the gates are grounded. For small signal: Grounded = A DC voltage, remember ? Note that the cascode is a common-gate amplifier. It has current input and output.

Here's an example: M1 is the cascode, it only "buffers" the current coming out of M2 which is a common source amplifier. In this configuration M2 will be a happy NMOS since it's Vds will be almost constant. This gets rid of much of the influence of the Rout of M2. There is of course still the Rout of M1 but that does not matter as M2 determines the current, not the cascode M1 !







simulate this circuit &ndash; Schematic created using CircuitLab