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9 OBDH Technology of Lunar Lander
The EMC design of device was an important guarantee for long-term and reliable operation. The three elements of EMC design were shielding, filtering and
grounding. Solving issue of anti-interference under condition of modular combination was the focus of electromagnetic compatibility design. The main source of
interference within a device was the conduction of signals and electromagnetic interference between components of circuit. The anti-interference design of a device
in OBDH subsystem could be classified into different levels including component,
circuit, unit and device. The anti-interference design in all levels should be conducted.
(1) Component level design
Generally, the guideline of components selection was to select low-speed integrated
circuits as far as possible, such as HC series and additional filter capacitor in power
input.
(2) Circuit and unit level design
The digital circuit was the most common broadband interference source, and the
transient ground current and the transient load current were the initial sources of
interference. Through the rational design of power and ground, decoupling of power
supply filter, layout and wiring, partition isolation, circuit layout, multi-layer circuit
board, and enhancement of signal integrity, it could be ensured that circuit boardlevel functions were performed normally while the external disturbance of circuit
board was minimized as far as possible.
(3) Device level design
The ground connection should be rationally dealt with. The ground should be classified and managed according to primary ground, secondary power ground, common
secondary ground and command ground. The order of unit combination should be
distributed according to electromagnetic interference, sensitivity and power.
The main approach of electromagnetic interference into devices was the I/O interface and the power line input. At the same time, the internal electromagnetic interference in devices could be coupled to the wire or cable connecting I/O interface and
power line, which could produce interference current and then conduct or radiate
outside the shield to cause conduction interference and radiation interference. A
good chassis shell had a good inhibition effect on electric field or plain wave so as
to increase interference loss. Therefore, the design of chassis should be integrated to
reduce the type and number of parts and ensure integrity of connection. The connection surfaces of chassis should be in concave and convex groove structure used to
block electromagnetic radiation channel and the thickness of metal material should
be enough to ensure good electric field shielding in all frequency bands.
There was electromagnetic coupling between lines. The best approach to reduce
interference and sensitive circuit was application of twisted pair and shielded line with
shield layer grounded to reduce input resistance of sensitive lines. The sensitive circuit
should apply the balanced line input to overcome interference from interference
source to sensitive line by the inherent common mode suppression ability of the
balanced line. The input and output of the DC/DC should be twisted as far as possible.
9 OBDH Technology of Lunar Lander
The EMC design of device was an important guarantee for long-term and reliable operation. The three elements of EMC design were shielding, filtering and
grounding. Solving issue of anti-interference under condition of modular combination was the focus of electromagnetic compatibility design. The main source of
interference within a device was the conduction of signals and electromagnetic interference between components of circuit. The anti-interference design of a device
in OBDH subsystem could be classified into different levels including component,
circuit, unit and device. The anti-interference design in all levels should be conducted.
(1) Component level design
Generally, the guideline of components selection was to select low-speed integrated
circuits as far as possible, such as HC series and additional filter capacitor in power
input.
(2) Circuit and unit level design
The digital circuit was the most common broadband interference source, and the
transient ground current and the transient load current were the initial sources of
interference. Through the rational design of power and ground, decoupling of power
supply filter, layout and wiring, partition isolation, circuit layout, multi-layer circuit
board, and enhancement of signal integrity, it could be ensured that circuit boardlevel functions were performed normally while the external disturbance of circuit
board was minimized as far as possible.
(3) Device level design
The ground connection should be rationally dealt with. The ground should be classified and managed according to primary ground, secondary power ground, common
secondary ground and command ground. The order of unit combination should be
distributed according to electromagnetic interference, sensitivity and power.
The main approach of electromagnetic interference into devices was the I/O interface and the power line input. At the same time, the internal electromagnetic interference in devices could be coupled to the wire or cable connecting I/O interface and
power line, which could produce interference current and then conduct or radiate
outside the shield to cause conduction interference and radiation interference. A
good chassis shell had a good inhibition effect on electric field or plain wave so as
to increase interference loss. Therefore, the design of chassis should be integrated to
reduce the type and number of parts and ensure integrity of connection. The connection surfaces of chassis should be in concave and convex groove structure used to
block electromagnetic radiation channel and the thickness of metal material should
be enough to ensure good electric field shielding in all frequency bands.
There was electromagnetic coupling between lines. The best approach to reduce
interference and sensitive circuit was application of twisted pair and shielded line with
shield layer grounded to reduce input resistance of sensitive lines. The sensitive circuit
should apply the balanced line input to overcome interference from interference
source to sensitive line by the inherent common mode suppression ability of the
balanced line. The input and output of the DC/DC should be twisted as far as possible.