Philips Launches Single-Chip RF Modulator

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 In order to ensure the set-top box is compatible with current TV sets, the set-top box must generate standardized VHF/UHF signals so as to drive the signals input by the TV antenna. 

The universal RF modulator TDA8822 launched by Philip can generate standardized VHF/UHF TV channel signals which meet the PAL or NTSC standards across the world with a single-chip solution. The functions of TDA8822 include I2C bus which can fully control the picture carried frequency， sound subcarrier frequency, video modulation depth, subcarrier deviation, and picture-sound ratio. Moreover, TDA8822 allows the insertion of externally modulated subcarriers such as NICAM or PAL B/G two-channel/stereo signals. Because this chip is equipped with a subcarrier synthesizer that is fully adjusted and does not need to be adjusted， and a built-in phase-locked loop that can control the picture carrier, the only required peripheral equipment is the variable capacitance circuit suitable for its RF oscillator and 4MHz quartz oscillator, and the 3.3V modulation voltage used by the varactor diode of this circuit is also directly controlled by the TDA8822 chip.

No matter when the engineers modulate the TDA8822, the non-locking detector in the phase-locked loop of the picture carrier will also automatically stop the RF output to prevent audio and picture interference. TDA8822 has been equipped with a buffered RF output, which can be used as two asymmetric outputs or one symmetrical output. The choice depends on the specific application scheme. Other functions of TDA8822 include clamping and clipping circuit for baseband video input (to prevent overmodulation), independent switch control of picture and sound carrier, and a programmable output port for general use. TDA8822 can also provide an on-chip test pattern generator for TV modulation.

National Semiconductor has recently launched an LM6172 voltage feedback dual operational amplifier. This is the industry's first dual operational amplifier with voltage feedback of 3000V per second. Compared with other competitors working under the power voltage of ±15V, the rate of LM6172 is close to more than twice than them. It not only has a rapid conversion rate but also has bandwidth with high benefit, drive circuit with high output, low distortion, low power consumption, and other characteristics.

Due to its conversion rate of 3000V per second, single-side gain bandwidth of 100MHz, and low consumption of 2.3mA of each channel, it is suitable to use it to handle and design video and signal. It is also suitable for the printer, electro-optical sensor, and sonar device, all of which need wide-range voltage. When designing a system needing a relatively wide dynamic range, high signal-to-noise ratio, and low total harmonic distortion, the extreme voltage range is very suitable and its extreme current can be applied to multiple channels.





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