Microtune, Plano, TXBroadband television and data reception has gained more attention in recent years mainly due to the advent of new digital TV standards and improved content such as high-definition television. At the same time, modern TV tuners in the United States, Europe, and much of the rest of the world must still receive legacy analog broadcasts until at least 2009 for terrestrial applications and probably longer for cable broadcasts.A typical cable TV spectrum has a limited input power range with small undesired-to-desired-signal (U/D) ratios, but contains a large number of channels resulting in possible distortion products [1,2]. Terrestrial, or off-air, TV spectrums have relatively few channels compared to cable, but they can have a wide range of input powers with the possibility of very large U/D ratios. For example, according to the North American digital television specification (ATSC A/74), there can be an interferer 6 channels (36MHz) away that has 57dB higher power than the desired signal [3]. Classically, both the tuner RF and IF AGC functions have been controlled by the demodulator, which only sees the desired channel and has no knowledge of interferers. This is acceptable for cable applications where the shape of the rest of the input spectrum can be inferred from the power of the desired signal. However, narrow tracking filters have not yet been integrated on silicon tuners, and there is a large frequency range of signals present at the input of the tuner active circuitry. The large interferer cannot be effectively filtered out on chip. Therefore, the tuner must provide its own RF AGC function to prevent compression, while letting the demodulator to control the IF AGC. Even the narrow tracking filters of discrete canned tuners have trouble attenuating such a large interferer. Many modern canned digital tuners need self-contained RF AGC control.The goal of the presented tuner is to use AGC to optimize the power levels at every block in the signal path. This provides the best possible RF performance by maximizing the input power, and therefore, the SNR, into every block without causing excessive distortion. By optimizing the signal path gain lineup in this way, the AGC does not need to distinguish between desired and undesired power levels. To accomplish this, a simple power detector with a few dB of range is required after every change in signal bandwidth (i.e., filtering), and gain control is provided at several locations in the signal path. Figure 11.3.1 shows the block diagram of the tuner. It is a dual-conversion architecture with external first-and second-IF SAW filters, and it consists of an input buffer and attenuator, a variable gain single-ended-input to differential-output LNA, an upconversion mixer, a variable gain image-reject downconversion mixer, an IF VGA, two fractional-N frequency synthesizers, two hybrid power/peak detectors, and a master AGC control block.All RF gain control is done in small digital steps controlled from up/down counters. As long as the step size is kept smal...