RF PCB - HD TV Tuner with embedded CPU
RF TV Tuner section design on a large mixed signal Printed Circuit Board (PCB) needs EM analysis of conducted and radiated interference from digital and power supply sections to meet sensitivity specs.
Printed Circuit Boards (PCB) for RF applications are typically combined with non-RF digital sections such as CPU, DSP, control circuits and power distribution networks.
Analyzing the effects of conducted and radiated interference from these sections on the sensitive RF portion of the PCB traditionally had been tedious, requiring the modification of the layout to isolate the portions to be EM simulated; followed by manual reconnection of the EM S-parameter results back to the circuit for circuit-EM co-simulation.
Fortunately, RFPro with automatic net, ground and component extractions from an imported ODB++ layout in ADS enables EM-circuit analysis of any selected portion of the PCB to identify and fix sources of interference before building hardware board turns.
PCBs for wireless and wired RF applications typically contain RF and non-RF sections such as CPU, DSP, control circuits and power distribution networks with their respective ground planes. They all come in together when imported as an ODB++ file as shown in Figure 1.
The RF design challenge here is how to selectively isolate the RF and selected non-RF sections for EM analysis to identify interference that may degrade RF performance before doing a time-consuming board turn.
Figure 1. Imported ODB++ of a HDTV tuner PCB with RF, CPU, DSP, control circuits and power distribution networks with their associated grounds.
Selecting the RF circuit and RF ground nets without modifying the layout that also includes lumped R, L, C circuit components along the path for EM analysis as shown in Figure 2.
Figure 2. Selecting the RF net (top), ground (bottom) and filtering capacitor along RF signal path from input connector to TV tuner IC without modifying imported ODB++ layout.
Selecting a suspected source of interference, e.g. neighboring digital signal lines and digital ground as shown in Figure 3 without modifying the layout for EM analysis.
Figure 3. Selecting neighboring digital lines (left) and associated grounds (right) as suspected source of interference to RF section without modifying the layout.
Designer can gain insights quickly by visualizing the current density on the PCB caused by a nearby digital line as shown in Figure 4.
Figure 4. Visualize interference from neighboring digital line on RF section by examining digital current density distribution.
Analyzing conducted and radiated digital interference on RF section by injecting realistic signals containing correct spectral power distribution into the respective digital and RF nets as shown in Figure 5. This requires tight integration between EM and circuit
Figure 5. Injecting realistic digital and RF signals containing correct spectral power distribution to analyze effects of conducted and radiated digital interference on the path of desired RF signal.
Fixing radiated interference with RF shield. Having identified the interfering source as radiated emission from the neighboring digital lines, the designer needs to quickly evaluate the effectiveness of adding a 3D RF shield component. This is shown in Figure 6 and requires the easy import of 3D components into the integrated circuit-EM analysis environment.
Figure 6. Shielding radiated interference by adding a 3D RF shield around TV tuner.
Analyzing effects of voltage fluctuations on CPU power distribution network on RF section as shown in Figure 7. Here the CPU power distribution network with associated grounds and decoupling capacitors are selected along with the RF signal path to be EM analyzed for undesired coupling and the RFPro EM results can be seen in the next section.
Figure 7. RFPro analyzes EM coupling between the CPU power distribution network (center) with associated decoupling capacitors and RF TV signal path. The EM S-parameter results are automatically connected with realistic signal sources in ADS.
o The tight integration of RFPro EM simulation interface in Advanced Design System (ADS) enables unprecedented ease in importing large PCB boards with RF sections for combined EM-circuit analysis.
o RFPro easy selection of nets and components without the need of layout modification for EM analysis is complemented by its automatic generation of equivalent PCB circuit from layout and connection of EM results with ADS circuit schematic.
o This allows the injection of realistic and spectrally correct signals from ADS into the EM analyzed structure to verify sensitivity performance of the TV tuner. Selective deactivation of components such as decoupling capacitors and ground vias to understand their impact on the design can be done in ADS without requiring new EM analysis and extraction as shown in Figure 8. This is especially useful for troubleshooting of causes of interference.
Figure 8. RFPro automatically extracts an EM S-parameter model of selected nets with interconnected R-L-C lumped components into an ADS sub-circuit for EM-circuit analysis using realistic signals and selective component and ground deactivation for troubleshooting of causes of interference.
Acknowledgements: The HD TV tuner design was provided by SECO S.p.A in Arezzo Italy demonstrating an example of efficient RF PCB design flow.
- RFPro enables PCBs with RF sections to be conveniently imported into ADS via the ODB++ file format for EM analysis of any selected nets and lumped RLC components without modifying the layout.
- RFPro automatically generates and extracts an EM sub-circuit of the above analyzed structure for use in ADS for injection of realistic signals and selective deactivation or substitution of RLC components and grounds. This is especially useful for troubleshooting of possible causes of interference from non-RF sources on the PCB.
- RFPro in ADS allows RF PCB designers to efficiently perform EM-circuit analysis on their RF sections of a larger mixed signal PCB to ensure optimal RF performance. This eliminates wasteful board turns and saves at least 1 to 3 months in the PCB development process.
Keywords:EM, RFIC, FOWLP, WiGig, mmWave, RF Module, RFPro, Integrated Antenna Array