Field Programmable ADC

General description:

Analog-to-digital converters (ADCs) usually have fixed specifications such as achievable bandwidth and resolution. When an ADC is required to cover multiple use-cases, or when not all requirements are yet known, an ADC can be selected or designed that covers all possible use-cases or possible requirements. However, this leads to a significantly higher power consumption than would be required for the individual use cases.

For these applications, Axiom IC is developing a field-programmable ADC (FPADC). It is a hybrid sigma-delta ADC with programmable loop filter coefficients, allowing a flexible trade-off between bandwidth, SNR and power consumption. This makes the FPADC ideally suited for applications that require flexibility (e.g. multi-standard radios), and for rapid prototyping. Two possible applications are shown in figure 1.

Even for applications where all ADC requirements are not known and fixed, the FPADC concept is very useful. Then, rapid prototyping can be done with an existing FPADC, after which a smaller derivative can be designed with fixed specifications. This leads to short design cycles with low risk.

Block diagram:

Figure 1: Block diagram of our FPADC

Features:

• Single ended current-mode input

• Programmable for a wide range of applications

• Both low-pass and band-pass operation

• 111 dB DR in 6 kHz

• 105 dB DR in 20 kHz

• 95 dB DR in 200 kHz

• 92 dB DR in 400 kHz

• 76 dB DR in 1.5 MHz

• Robust to full-scale out-of-band interferers

• Area: 0.4 mm²

• Technology: 65 nm CMOS

Applications:

• Radio receivers

  • AM, FM, DAB, Bluetooth, WLAN, TV, DVB

  • Multi-standard

  • Future standards

• High-resolution audio

• Programmable mixed-signal system

Figure 2: Two possible applications of a field-programmable ADC (FPADC)

Detailed description:

The FPADC features a single-ended current-mode input. Multiple ADCs can be used to convert differential and I/Q signals. The ADC tolerates full-scale out-of-band signals, to lower input filter requirements. The ADC itself has a first-order low-pass transfer with programmable corner frequency. A block diagram of the FPADC is shown in figure 2.