Speaking of system-level integration, such programmable and reconfigurable analog building blocks have also been implemented in system-on-a-chip (SoC) design. With accompanying user-friendly CAD tools and Windows-based IDEs, engineers can now define a complete analog circuit on a PC screen and download the circuitry onto the associated chip just by clicking a button.
More on-chip functional blocks, higher bandwidth, and infinite reconfigurability are the future. Meanwhile, integrated analog front ends (AFEs) are being optimized to deliver dedicated solutions for specific systems. For multichannel applications, several AFEs are being packed on one chip. Likewise, audio codecs are driving the mixed-signal front to new heights.
Audio codecs. For superior sound quality in consumer products, audio codecs are packing 24-bit stereo ADC and DAC converters with 96-kHz and better sampling rates at 3-V and below supply voltages on-chip. Headphone amplifiers also are integrated, along with digital techniques to control the sound effects. All necessary software is embedded on-chip to make the product designer's job simple. In addition, the power consumption is being driven to a new low. Makers like Cirrus Logic (www.cirrus.com) are looking at power consumption below 19 mW in playback mode.
Nanopower power comparators. Like amplifiers, comparators are getting faster at low voltages. In fact, nanopower comparators with built-in voltage references are demonstrating switching speeds in the range of tens of nanoseconds. In speed-critical applications, single-supply, 3-V comparators are touting sub-5-ns speed. The comparators will take advantage of progress in CMOS and CB transistors to keep getting better at even lower supply voltages.
Dedicated AFEs. While the focus is on making the AFEs as complete as possible, they also are being optimized for specific applications like set-top boxes, cable/ADSL modems, imaging, and other systems. As these parts bring higher-resolution converters and wider bandwidth amplifiers on board, they also are providing seamless links to follow on microcontrollers and DSPs. Several complete AFEs are being integrated on a CMOS die.
Reconfigurability. The functionality and complexity of in-system programmable analog and field-programmable analog arrays (FPAAs) are on the rise, as makers promise to broaden the product portfolio to give designers some choice. SRAM cells are being added to existing EEPROM cells on-chip to enable infinite reconfigurability during system operation.
Mixed-Signal SoCs. Integrating analog and mixed-signal functions in very deep-submicron CMOS poses many challenges. Unlike digital, analog transistors don't readily scale, and the problem becomes worse as voltages fall below 1 V and clock rates hit gigahertz frequencies. Although biCMOS, especially SiGe biCMOS, initially will come to the rescue, the progress in CMOS to be presented at next month's International Solid-State Circuits Conference raises hopes. Clever circuit techniques like switching op amps instead of filter capacitors and implementing extended-drain technology will get the designers to pure CMOS integration, as insulators are replaced with high-k dielectric materials and copper interconnects become standard in the next few years.
