Traditionally, the packaged integrated circuit (IC) has been much larger than the IC itself because standard packages must also contain the lead-frame and bond wires. That wasn’t an issue for decades because space wasn’t an issue in most applications, but more recently, a couple of trends have been driving precision analog devices toward smaller packages in sizes that approximate the size of the dies themselves.
Most obvious is the move toward smaller size in the end equipment. Equipment that used to have its own room became portable and even wearable. These space-constrained applications are enough to drive a manufacturer of standard analog devices such as op amps, analog-to-digital converters (ADC), or digital-to-analog converters (DAC) to offer them in smaller packages. But new applications are also spurring the development of products that pack multiple channels into a single tiny device: so-called “high-density” products.
Take the internet, for example. Its backbone is a high-speed optical-fiber network that must continually be upgraded to satisfy the never-ending demand for increased bandwidth. New optical switching technologies such as the reconfigurable optical add-drop multiplexer (ROADM) and wavelength selective switching (WSS) technology are helping to drive throughput increases at network switching nodes. However, a WSS system requires massive arrays of DACs to help route signals between arrays of optical fibers.
The DACs operate as square-wave generators at different amplitudes. Each DAC is configured with a high and low code; an external trigger signal toggles the output between the two codes. This function is repeated hundreds of times over many settings in any one system—thus the need for extreme integration. These systems are always space-constrained, so the more DACs per package, the better. Figure 1 shows a single DAC in a WSS system.