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.
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
The functional block diagram is shown below.