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Download PRACTICAL ANALOG DESIGN TECHNIQUES
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HARDWARE DESIGN TECHNIQUES GROUNDING AND DECOUPLING MIXED-SIGNAL ICS WITH LOW DIGITAL CURRENTS Sensitive analog components such as amplifiers and voltage references are always referenced and decoupled to the analog ground plane. The ADCs and DACs (and other mixed-signal ICs) with low digital currents should generally be treated as analog components and also grounded and decoupled to the analog ground plane. At first glance, this may seem somewhat contradictory, since a converter has an analog and digital interface and usually has pins designated as analog ground (AGND) and digital ground (DGND). The diagram shown in Figure 10.17 will help to explain this seeming dilemma. PROPER GROUNDING OF MIXED-SIGNAL ICs WITH LOW INTERNAL DIGITAL CURRENTS VA VD FERRITE BEAD A LP LP CSTRAY RP AIN/ OUT ANALOG CIRCUITS LP R B CSTRAY IA ID AGND A SEE TEXT RP DIGITAL CIRCUITS DATA A RP D VD VA SHORT CONNECTIONS BUFFER GATE OR REGISTER DATA BUS CIN ≈ 10pF RP LP DGND A A = ANALOG GROUND PLANE VNOISE D D = DIGITAL GROUND PLANE Figure 10.17 10.21
