I'm currently designing a mixed-signal PCB for a client and I've been reading a lot about signal integrity and most of the books recommend a 4 layer board (or more) because of the noise resistance from having a solid ground plane and reduced routing.
The board in question has two 16-bit ADCs and two 16-bit DACs with OP amps in the analog section, a microcontroller with some level shifters and mosfets in the digital section, and two DC/DC converters and an LDO regulator in the power section. Space is not much of a constraint, but having high resolution and low noise in the analog section is important. There's an I2C and an SPI bus running between the digital section and the edge of the analog section, operating at less than 10 MHz.
Routing wise I can totally get this board done in 2 layers. Will I really notice a huge difference in signal integrity with a 4 layer board and dedicated ground plane? Is it worth the extra cost? I'm leaning towards 4 but I'd like to hear your opinions.
Thanks in advance guys.