Design Of The Key Circuit In Analog Front End Of High Definition Television

Analog front-end (AFE) has been widely used in the wireless communication receiver, digital television set-top box, digital camera, and so on. In particular, AFE directly influences the quality of image in high definition television (HDTV). On the other hand, variable gain amplifier and filter are the essential cell circuits of AFE in HDTV. Therefore, it is important to study the circuit designing of variable gain amplifier and filter of AFE in HDTV.In this paper, a high-linearity programmable gain amplifier is designed by employing a new current-mode amplifier with programmable resistor-network feedback. The programmable gain amplifier (PGA) has a voltage gain varying from 3 dB to 33 dB with 3 dB gain step and a bandwidth of 82.3 MHz. Compared to conventional voltage amplifier, the constant bandwidth, high linearity and precision, and low power are achieved. The variation of voltage gain of the PGA can be realized by switched resistor-network, which is digitally controlled.Moreover, a new fully differential operational amplifier is proposed. The voltage and current common mode feedback is realized at the same time in this fully differential operational amplifier. Compared to similar kinds of amplifiers, this amplifier exhibits high phase margin, indicating that it is not apt to excitation. In addition, the amplifier has the feature of high stabilization of quiescent point. Furthermore, the second-order low-pass Butterworth filter is designed based on above fully differential operational amplifier, and passive resistor and capacitor by the method of second-order low-pass passive filter equivalent transformation. The band-pass filter is also designed by using the method of cascade connection of first-order high-pass and first-order low-pass. Simulation of PGA and filter shows that performance of the circuits satisfies the design requirements.Finally, the PGA and filter layout are designed and verified.