Comparing PSoCs and MCUs in digital TV design
In this Product How-To article, Ronak Desai of Cypress describes the design challenges in digital TV applications and compares the use of microcontrollers and the company’s Programmable SoC architecture in dealing with roadblocks to efficient implementation.
Microcontrollers are used widely in current digital TV designs to provide mechanisms to direct the tuner to access specific frequencies, receive IR inputs from remote controls, vary the speaker sound output, controls the front panel mechanical switches and LCD/LED displays.
In this article, the use of programmable SOCs devices will be described as an alternative in the design of a single board solution for tuning analog and digital tuner frequency using I2C interface and receive IR inputs from the remote control using PSoC Creator’s IR receiver component to vary speaker sound output via a direct drive LCD/ LED display for front panel. It will also show how the designer can use a PSoC’s capacitive sensing technology to replace mechanical buttons on the keypad.
Using an MCU to build a digital TV tuner
As shown in Figure 1, below, typically, an 8- or 16-bit microcontroller is used for this type of application. It uses external EEPROM on the board to store information like the last channel viewed and favorite channels. It receives user inputs from the remote control through an IR receiver operating at 38 KHz frequency.
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The microcontroller also displays channel and volume information on an LCD module or front panel display, as well as controls the aspect ratio of the TV screen (4:3 or 16:9), adjusts the audio (Volume control, Equalizer control) and video (Brightness, Contrast) parameters of the TV.
A smartcard interface in the TV is used to decode the user subscription. The smartcard communicates to the microcontroller through an I2C Interface. The Mechanical Buttons are used for the front panel key pad to show case functions like CHA+, CHA-, VOL+, VOL- etc.
Digital Tuner Block: As shown in Figure 2 below, the microcontroller communicates with the TV tuner through an I2C (SCL, SDA) interface and tunes the Analog and Digital Tuner at IF (Intermediate frequency) frequency, which is 38.9MHz for the PAL (Phase alternate Line) region. The digital tuner has an internal digital demodulator, which provides direct CVBS (Composite video broadcast signal) and Audio left and right output.
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The user selects television channels either using the remote control or using a front panel keypad. If the user selects Channel #1, for example, it is 48.25MHz, and the microcontroller tunes the local oscillator at 87.15MHz (48.25MHz + 38.9MHz = 87.15MHz) using the I2C interface. Thus, the output of the mixer will be 38.9MHz (Local Oscillator Frequency: 87.15MHz - Input Frequency: 48.25MHz = Intermediate frequency: 38.9MHz), which is the IF frequency. The tuner will provide the IF with the video and audio information of Channel#1.