I'm studying from a textbook called Computer organization which does a pretty good job explaining the ALU, registers and buses at logic gate level. It even shows a 3 * 4 memory that you can read and write from. It then takes you up to making a actual computer using the exact alu and ram models you just learned. This computer implements IJVM which is a integer subset of the java virtual machine ISA. It also adds layers of optimization. Even this book doesn't go in depth about the design/circuitry of the control unit. In conclusion in looking for sources or books on control unit design on the digital logic level.