Design Of PGA And AGC Loop In DAB Receiver

Recently, digital mobile TV industry has rapidly grown in China. It is expected to become a big market. It is also very important for the development of Chinese integrated circuit industry. The digital mobile TV receiver chip proposed in this paper is based on DAB/DMB standard. In this paper, a programmable gain amplifier is designed and an auto gain control algorithm is proposed. They are all used in the receiver chip.In the DAB/DMB receiver, the programmable gain amplifier is usually required to achieve high linearity and constant bandwidth etc. In this paper, the digitally programmable-gain amplifier is not realized using voltage-mode amplifier. Constant bandwidth and high linearity are achieved by using a new current-mode amplifier with programmable resistor-network feedback. The PGA has a voltage gain varying from 0dB to 15.5dB with a bandwidth of 1.4MHz. The linear-in-dB gain is achieved by using digital control code. With 1 V_pp output, the third-order intermodulation of the PGA is 65.9dB at 0.2MHz and 0.3MHz. The circuit dissipates 2.38mW from a 3.3V supply.Auto gain control is a key element in the receiver system. The function of the auto gain control loop is to automatically adjust the gain of the receiver so that the signal can be processed correctly regardless of the actual signal strength. The auto gain control algorithm in this paper is implemented by using digital circuit. The gain of the low noise amplifier and the programmable gain amplifier is controlled by the auto gain control loop. The auto gain control loop can maintain stable settling time and fast control.The circuit in this paper is fabricated in a 0.18μm CMOS technology. The receiver chip has been tested and it can work successfully.