Direct-Conversion Video Receiver With DC Offset Cancellation
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Solution Overview
Problem
Existing silicon tuners for analog video reception face challenges in achieving a balance between image rejection and power consumption, often resulting in compromised performance at low power or reasonable performance at high power, making them unsuitable for small portable devices.
Innovation Solution
The development of an integrated analog video receiver with a direct-conversion tuner that converts broadcast-frequency signals directly to baseband, incorporating offset cancellation circuitry and adaptive image rejection to improve performance, and a power management system to reduce power consumption during superfluous video intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a direct-conversion tuner architecture is used to reduce power consumption and size, then power consumption and device size are reduced, but DC offset and image rejection performance deteriorate
Solution Approach 1:
The patent extracts and removes the DC offset component from the signal path using a dedicated cancellation circuit. This circuit separately processes the offset component and subtracts it from the main signal, effectively eliminating the harmful DC offset without affecting the overall direct-conversion architecture's low power and compact benefits
Solution Approach 2:
The patent introduces an intermediary DC offset cancellation circuit between the mixer and subsequent processing stages. This intermediary circuit acts as a mediator that handles the DC offset problem without requiring changes to the main direct-conversion tuner architecture, thus preserving power efficiency while improving performance
2Volume of moving object
If integrated passive components are used in silicon tuners to reduce size, then device size is reduced, but image rejection performance deteriorates
Solution Approach 1:
The patent changes the operational parameters of the direct-conversion mixer by carefully controlling the local oscillator frequency and phase relationships. This parameter optimization compensates for the limitations of integrated passive components, achieving acceptable image rejection without requiring large external filters
Solution Approach 2:
The patent replaces the traditional mechanical/approach of using large external channel selection filters with an electronic solution based on direct-conversion mixing and digital/baseband processing. This substitution eliminates the need for bulky passive filter components while maintaining selectivity through electronic means
3Reliability
If DC offset cancellation circuitry is added to improve performance, then image rejection performance is improved, but device complexity increases
Solution Approach 1:
The patent merges the DC offset cancellation function with the existing mixer and baseband processing circuitry. The offset cancellation is implemented using the same signal paths and components already present in the direct-conversion architecture, thereby adding minimal complexity while achieving effective offset removal
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.