Differential Transimpedance Amplifier Without Coupling Capacitors
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Solution Overview
Problem
Existing transimpedance amplifier circuits require additional amplifiers and increased supply voltage, leading to increased noise, complexity, and costs, while also necessitating additional components that degrade high-frequency behavior and noise performance.
Innovation Solution
A transimpedance amplifier design where the first and second amplifier sections share a common supply voltage and current source, with differential input connections to minimize noise and circuit complexity, and an operating point adjustment mechanism to set the photodiode voltage, eliminating the need for coupling capacitors and reducing bandwidth degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If additional amplifiers are added at the input of the transimpedance amplifier, then the amplification capability is improved, but the noise behavior deteriorates and circuit complexity increases
Solution Approach 1:
The patent merges the amplification function directly into the transimpedance amplifier stages themselves, eliminating the need for separate input amplifiers. The first and second amplifier sections perform both the initial signal amplification and the transimpedance conversion function, thereby avoiding additional noise sources and reducing circuit complexity while maintaining amplification capability.
2Power
If additional amplifiers are added at the input, then the amplification capability is improved, but circuit complexity increases
Solution Approach 1:
The patent combines multiple functions into the amplifier sections: the first and second amplifier sections simultaneously perform signal amplification, transimpedance conversion, and photodiode biasing. This functional integration eliminates the need for separate input amplifiers and reduces overall circuit complexity while maintaining full amplification capability.
Solution Approach 2:
The amplifier sections are designed to perform multiple functions: they amplify the input signals, convert current to voltage (transimpedance function), and provide biasing for the photodiodes. This multi-functionality reduces the number of required components and simplifies the overall circuit architecture.
3Power
If additional amplifiers are added, then the amplification capability is improved, but supply voltage must be increased
Solution Approach 1:
The patent merges the amplification and transimpedance conversion functions into the same stages, allowing the circuit to achieve full amplification capability without requiring additional voltage headroom for separate amplifier stages. The common current source and shared supply voltage architecture enables efficient voltage utilization.
4Reliability
If coupling capacitors are added to the input, then the photodiode connection is improved, but high-frequency behavior deteriorates and noise increases
Solution Approach 1:
The patent removes coupling capacitors from the input path by directly connecting the photodiodes to the amplifier inputs. The amplifier sections are designed to directly accept and amplify the photodiode currents without requiring capacitive coupling, thereby eliminating the bandwidth-limiting and noise-introducing effect of capacitors while maintaining reliable photodiode connection.
5Reliability
If additional components are added to the input path, then the photodiode connection is improved, but noise increases and high-frequency behavior deteriorates
Solution Approach 1:
The patent removes unnecessary components from the input path by directly connecting the photodiodes to the amplifier inputs. The amplifier sections are designed to directly process the photodiode currents without requiring additional coupling or blocking components, thereby minimizing noise sources and preserving high-frequency response while maintaining reliable connections.
Data Source
AI summary
The invention relates to a circuit containing a transimpedance amplifier for converting two input currents into two output voltages, having a first amplifier part containing a first input, to which a first input voltage is applied, and into which a first input current flows, and having a second amplifier part containing a second input, to which a second input voltage is applied and into which a second input current flows, wherein the first amplifier part and the second amplifier part are connected to a common supply voltage, the first amplifier part and the second amplifier part are connected to a common current source, the input of the first amplifier part and the input of the second amplifier part have a differing direct voltage, and the first amplifier part and the second amplifier part are designed such that an output voltage of the first amplifier part is proportional to the input current of the first amplifier part and an output voltage of the second amplifier part is proportional to an input current of the second amplifier part.