What is the interleaving technique for ADCs and how does it increase effective sampling rate?
Interleaved ADCs
The timing mismatch spur amplitude is approximately: Spur_dBc ≈ 20·log10(π × f_in × Δt), where f_in is the input frequency and Δt is the timing mismatch. For 1 ps timing skew at 2 GHz input: spur level = 20·log10(π × 2×10⁹ × 1×10⁻¹²) = -50 dBc. This shows why timing calibration is critical at high input frequencies. Sub-100 fs calibration accuracy is needed for > 70 dBc spur suppression at multi-GHz input frequencies.
| Parameter | Pipeline ADC | SAR ADC | Sigma-Delta ADC |
|---|---|---|---|
| Sample Rate | 100 MS/s - 10 GS/s | 1-100 MS/s | 10 kS/s - 50 MS/s |
| Resolution | 8-14 bits | 10-20 bits | 16-24 bits |
| Latency | Several clock cycles | 1 conversion cycle | Many cycles (decimation) |
| Power | High | Low-moderate | Low |
| Typical RF Use | Direct sampling, DPD | Control, monitoring | Audio, baseband |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
Frequently Asked Questions
How many channels can I interleave?
Practical TI-ADCs use 2 to 64 channels. Monolithic TI-ADCs (single chip): typically 2-4 channels. Board-level interleaving: up to 16-64 channels (used in oscilloscopes and wideband SIGINT receivers). More channels increase the calibration complexity and the number of interleaving spur frequencies.
Can I interleave ADCs from different manufacturers?
Technically possible but extremely difficult. The mismatches between different ADC types are large and temperature-dependent, requiring sophisticated calibration. In practice, TI-ADCs use identical ADC channels on the same die (monolithic interleaving) for best matching.