Using microcontrollers in CATV applications--Page 3.
RF signal measurement uses the following blocks:
Figure 4. PSoC in RF signal measurement application.
Optical signal measurement uses the following blocks:
PSoC in optical signal measurement.
Implementation of PSoC in RF and Optical signal measurement:
PSoC is a combination of a microcontroller with programmable logic and high performance analog to digital conversions and commonly used fixed-function peripherals. PSoC is an 8-/16-/32-bit MCU architecture with up to 64KB Flash, 8KB SRAM, and 2KB internal EEPROM.
PSoC has n internal configurable delta-sigma ADC with 8- to 20-bit resolution, 8-bit DAC, four 16-bit configurable timers, four 16- bit PWMs, clock, multiplexer, comparators and I2C interface to be used for RF signal and optical signal measurement and calculating different parameters of the RF signal. It also has an internal and configurable TIA for optical signal strength measurements.
As an ultra-low power device, in low power mode, it consumes <1µA current, making it useful for battery-based applications. PSoC has an internal PGA, comparators, and configurable delta-sigma ADC with 8- to 20-bit resolution and sample rates up to 192ksps. The ADC is used to measure the different analog inputs including AC Line voltage input, battery input, and RSSI input in RF signal measurements.
An internal 8-bit DAC can be used for controlling the volume of the speaker and perform a mute function. PSoC can also directly drive LED and LCD displays (Segment LCD, Graphic LCD and Character LCD displays) for displaying channel and volume information. With an operating rage of 1.71V to 5.5V, PSoC can easily interface with external peripherals for other applications. PSoC also has an internal RTC component for real-time measurement and an internal system clock to eliminate the need for external clock/oscillator circuitry.
The PSoC Creator IDE provides a tool for designing the interfaces and logic. PSoC Creator uses component blocks for designing the PGA for analog sensors and other inputs as well as I2C, SPI, PWM, TIA, CLK, MUX, TIMERS, USB, and CMP functions used in CATV applications. PSoC Creator also enables customer to tap into an entire tools ecosystem with integrated compiler tool chains, RTOS solutions, and production programmers. Designers can create and share user-defined, custom peripherals using a hierarchical schematic design, as well as automatically place and route select components and integrate simple glue logic, normally located in discrete multiplexers.
PSoC supports the USB 2.0 interface, enabling the transfer of signal information.
It also supports capacitive sensing technology to enable the replacement of mechanical buttons on the keypad with PCB pads, which acts as a buttons. PSoC supports sliders for volume up/down function as well as proximity sensing so the front keypad light can be activated whenever a user places a hand near the keypad.
To perform the key functions required for CATV applications in the most cost-effective manner, a microcontroller must provide sufficient performance as well as integrate Flash and SRAM memory, EEPROM, TIA, analog and digital peripherals, DAC for volume control, capacitive sensing for the front panel keypad, and an RTC for timer and sleep functions.
Product calibration at different signal levels is a design challenge for system designer. PSoC has internal EEPROM up to 2KB to store product calibration parameters.
RF and microcontroller-based mixed-signal board design must meet audio and video performance requirements. PSoC is a combination of a microcontroller with programmable logic and high performance analog to digital conversions. Using PSoC in the design will improve the board performance by using internal programmable analog and digital peripherals. Filter implementations using PSoC improve signal quality and help improve system noise cancellation.
Low-cost front panel design is required as well, supporting features like button and LED interfaces. Using PSoC’s capacitive sensing technology, button, slider, and proximity sensing controls can be implemented for the front panel design. Meeting key capacitive sensing performance parameters like SNR (signal-to-noise ratio) with nearby LEDs (PWM-based) on the front panel is another design challenge for system designer. SNR is also affected by RF and power supply interference. Furthermore, certifying this electro-mechanical design with EMI/EMC standards is a design challenge for system designer.
As this system involves electro-mechanical construction, designing a compact and cost-effective electro-mechanical system for CATV is a design challenge for system designer. It is advantageous to choose a microcontroller with One Time Programmable (OTP) features to prevent reverse engineering of the firmware by competitors and hackers.
System limitations and potential improvements
PSoC supports capacitive sensing technology that replaces mechanical button with a capacitive sensing-based keypad. This reduces failures due to mechanical buttons and provides better product reliability.
PSoC Creator supports CapSense SmartSense components which autotune the sensitivity of capacitive sensing-based buttons and sliders without requiring manual tuning for these controls. Implementations of touchscreen-based designs on the front panel instead of an LCD display or keypad also provide better user interface and flexibility.
Interfaces for external devices like iPod / iPhone enable the microcontroller to communicate to the iPod/ iPhone using a UART or USB interface. Users can communicate to iPod / iPhone devices through the microcontroller interface and transfer signal information.
Failure Analysis and Returned Materials: Increasing the number of internal and external interfaces on the board is going to increase the number of ways that an intruder can create havoc on the system. This is one of the single largest limitations of this embedded system.
Cable Television is using microcontrollers for RF and optical strength measurements, user interfaces (keypad, LED, LCD / graphical display), and audio volume control. PSoC is a combination of microcontroller and ASIC that can reduce complete product cost (by reducing the BOM cost) and project cost (simplified application design using PSoC Creator).
About the Author
Ronak Desai is a Staff Engineer at Cypress Semiconductor with nine years of industry experience. He has a BE in Electronics and Communication from Mumbai University, India. He is part of the Development Kits Group and is based out of Bangalore, India. You can reach Ronak at email@example.com.