Cross-Coupled Differential TIA for Stable 10 GHz Bandwidth

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Solution Overview

Problem

Conventional differential transimpedance amplifiers based on operational amplifiers in negative feedback topology have limited bandwidth, typically operating only up to a few mega-Hertz due to stability considerations, which restricts their application in modern CMOS process technology.

Innovation Solution

A differential transimpedance amplifier design utilizing a complementary differential topology with common-gate amplifiers and cross-coupling capacitors, along with bias and load networks, to achieve a wider bandwidth, specifically up to ten giga-Hertz operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an operational amplifier is configured in a negative feedback topology with a feedback resistance, then the transimpedance amplifier can provide stable gain control, but the bandwidth is limited to a few mega-Hertz due to stability considerations

Engineering Contradiction:

ImprovestabilityVSAvoidbandwidth

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent extracts the feedback mechanism from the traditional operational amplifier configuration. By removing the negative feedback topology and using direct common-gate amplifier stages with cross-coupling capacitors, the design eliminates the stability-bandwidth tradeoff that plagues feedback-based transimpedance amplifiers, achieving both stability and high bandwidth simultaneously

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent substitutes the feedback control mechanism (analogous to a mechanical control system) with a direct amplification architecture. The common-gate amplifier stages with cross-coupling capacitors provide the necessary gain and stability without requiring feedback, thereby eliminating the bandwidth limitation imposed by feedback stability constraints

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If a differential operational amplifier is used in a feedback topology, then the amplifier can provide differential signal amplification, but the operational bandwidth is restricted to a few mega-Hertz

Engineering Contradiction:

Improvedifferential signal capabilityVSAvoidoperational bandwidth

Core Design Contradiction:

Adaptability or versatilityVSSpeed

Solution Approach 1:

The patent segments the differential amplification function into separate common-gate amplifier stages. Each transistor (MN1, MN2, MP1, MP2) operates as an independent common-gate stage with its own input and output nodes, connected through cross-coupling capacitors. This segmentation allows each stage to operate at high speed while collectively providing differential signal amplification capability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of using the conventional approach where differential amplification is achieved through feedback topology, the patent inverts the approach by using direct-coupled common-gate stages with cross-coupling capacitors. This inverted architecture achieves differential signal capability without the bandwidth-limiting feedback mechanism

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS11075607B1High-speed differential transimpedance amplifier and method thereof

Publication Date: 2021.07.27 REALTEK SEMICON CORP

AI summary

A differential transimpedance amplifier includes a first pair of common-gate amplifiers having a first NMOS transistor and a second NMOS transistor configured in a cross-coupling topology using a first capacitor and a second capacitor, a second pair of common-gate amplifiers comprising a first PMOS transistor and a second PMOS transistor configured in a cross-coupling topology using a third capacitor and a fourth capacitor, wherein an output of the first pair of common-gate amplifiers and an output of the second pair of common-gate amplifiers are coupled via a fifth capacitor and a sixth capacitor.