Direct-Conversion Video Receiver With DC Offset Cancellation
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Solution Overview
Problem
Conventional silicon tuners for analog video reception face challenges in achieving a balance between image rejection and power consumption, leading to compromised performance at low power or high power consumption, making them unsuitable for small portable devices.
Innovation Solution
A direct-conversion analog video receiver architecture that includes a direct-conversion tuner, offset canceller, and adaptive image rejection filter, which converts broadcast-frequency signals directly to baseband, reduces power consumption by using a low-pass filter instead of a channel selection filter and dynamically cancels offsets and rejects images, while a power manager powers down components during superfluous video intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete tuner cans are used for analog video reception, then robust performance is achieved, but power consumption increases to two to three watts and size increases
Solution Approach 1:
The patent replaces the mechanical/discrete component-based tuner can architecture with an integrated silicon-based electronic system. The direct-conversion receiver architecture integrates mixing, filtering, and signal processing functions into a unified silicon implementation, eliminating the need for discrete tuner cans while achieving lower power consumption and smaller size suitable for portable devices
Solution Approach 2:
The patent combines multiple previously separate functions (channel selection filtering, mixing, and signal processing) into a single integrated direct-conversion receiver architecture. By merging the channel selection filter with the mixing stage and implementing everything in silicon, the system achieves compact form factor and reduced power consumption while maintaining robust video reception performance
2Ease of manufacture
If silicon tuners with superheterodyne architecture are used, then integrated circuit implementation is achieved, but image rejection performance deteriorates due to poor integrated passive performance
Solution Approach 1:
The patent segments the receiver architecture into distinct functional blocks: a direct-conversion mixing stage that converts RF directly to baseband, followed by separate digital signal processing stages for image rejection and channel selection. This segmentation allows each stage to be optimized independently, with digital processing handling image rejection tasks that are difficult to achieve with analog integrated passives
Solution Approach 2:
The patent replaces analog image rejection filtering (which suffers from poor integrated passive performance) with digital signal processing techniques. By converting the signal to digital form and applying digital filters, the system achieves superior image rejection performance that is not limited by the quality of integrated passive components
3Use of energy by moving object
If low-pass filter is used instead of channel selection filter, then power consumption is reduced, but filtering capability must be maintained
Solution Approach 1:
The patent replaces the analog channel selection filter with a digital filtering implementation. After the direct-conversion mixing stage produces baseband signals, digital filters are applied to perform channel selection and reject out-of-band signals. This substitution of digital for analog filtering significantly reduces power consumption while maintaining or improving filtering capability through the programmable nature of digital filters
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables efficient, low-power analog video reception with improved image rejection and reduced power consumption, making it suitable for small portable devices like mobile phones and laptops.
Implementation Method 1
a mixing circuit to mix an analog video signal with a sinusoid to generate a frequency-shifted analog video signal
Implementation Method 2
an offset cancellation circuit to obtain a sample of the frequency-shifted analog video signal during a first time interval and, based on the sample, generate an offset cancellation signal that, when summed with the frequency-shifted analog video signal, reduces a substantially time-invariant offset in the frequency-shifted analog video signal
Data Source
AI summary
An analog video receiver implemented in an integrated circuit device. The analog video receiver includes a mixing circuit to mix an analog video signal with a sinusoid to generate a frequency-shifted analog video signal, and an offset cancellation circuit to obtain a sample of the frequency-shifted analog video signal during a first time interval and, based on the sample, generate an offset cancellation signal that, when summed with the frequency-shifted analog video signal, reduces a substantially time-invariant offset in the frequency-shifted analog video signal.