Flexible Bandgap Reference Circuit with Adjustable PTAT-CTAT Current Summing

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Solution Overview

Problem

Existing bandgap voltage reference circuits face challenges with fixed, non-adjustable output voltages, startup issues, and noise transients, particularly at high supply voltages, due to their reliance on silicon bandgap voltage and logarithmic temperature dependencies.

Innovation Solution

A voltage reference circuit utilizing PTAT and CTAT currents, generated through separate resistors and summed to produce an output voltage greater than the silicon bandgap voltage, with a startup network that operates at high supply voltages and avoids noise transients and false triggering, using MOSFET current mirrors and diode-connected BJTs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a fixed bandgap voltage reference circuit is used, then the reference voltage is stable and temperature-compensated, but the output voltage cannot be adjusted and may cause startup issues at high supply voltages

Engineering Contradiction:

Improvereference voltage stabilityVSAvoidoutput voltage adjustability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The reference voltage generation is segmented into multiple independent current sources (PTAT current generator, CTAT current generator) that can be selectively activated. This allows the circuit to provide a fixed stable reference when needed while enabling adjustment by selecting different current combinations, resolving the contradiction between stability and adjustability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit transitions from a static fixed bandgap reference to a dynamic configurable reference system. Control logic dynamically selects and combines different current sources based on required output voltage levels, enabling both stable operation and flexible adjustment across different operating conditions.

Inventive Principle:

Principle #15Dynamics

2Ease of operation

If a crude bandgap circuit is used for startup, then the circuit can start up properly, but noise transients and false triggering occur

Engineering Contradiction:

Improvestartup capabilityVSAvoidnoise transients

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

A dedicated startup circuit is implemented that pre-establishes proper operating conditions before the main reference circuit activates. This preliminary action ensures clean startup without noise transients by carefully controlling the activation sequence of current sources and providing initial bias currents that prevent false triggering.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The startup circuit acts as an intermediary between the power supply and the main reference circuit. It provides a clean transition path that isolates the main circuit from startup noise and transients, allowing proper initialization without introducing harmful noise effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If the reference voltage is set to silicon bandgap voltage, then temperature compensation is achieved, but the output voltage does not match desired reference levels and flexibility is lost

Engineering Contradiction:

Improvetemperature independenceVSAvoidreference voltage flexibility

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The circuit changes the parameter of reference voltage magnitude while maintaining temperature independence. By adjusting the ratios and combinations of PTAT and CTAT current sources, the output voltage can be tuned to different desired levels while the temperature compensation mechanism remains effective, resolving the contradiction between fixed bandgap voltage and flexible reference levels.

Inventive Principle:

Principle #35Parameter changes

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 provides a freely adjustable, accurate reference voltage that maintains stability across a wide temperature range and high supply voltages, reducing startup issues and noise transients, with improved accuracy and flexibility compared to conventional bandgap reference circuits.

Implementation Method 1

generate the proportional to absolute temperature (PTAT) current across a resistor with differential in the base-emitter voltage (ΔVBE) of two bipolar junction transistors (BJTs)

Methodology Applied

Scientific EffectPTAT (Proportional to Absolute Temperature):

Implementation Method 2

the complementary to absolute temperature (CTAT) dependence of a base-emitter voltage to temperature is used

Methodology Applied

Scientific EffectCTAT (Complementary to Absolute Temperature):

Implementation Method 3

differential in the base-emitter voltage (ΔVBE) of two bipolar junction transistors (BJTs) with different emitter areas

Methodology Applied

Scientific EffectBase-emitter voltage differential (ΔVBE):

Data Source

PatentUS10831228B2Apparatus and method for high voltage bandgap type reference circuit with flexible output setting

Publication Date: 2020.11.10 APPLE INC

AI summary

An apparatus and method for a voltage reference circuit with flexible and adjustable voltage settings. A voltage reference circuit, comprising a PTAT Current Generator configured to provide current through a first resistor, a CTAT Current Generator configured to provide a CTAT current through a second resistor, a PTAT-CTAT Adder circuit configured to sum the PTAT current, and the CTAT current, wherein said sum of the PTAT and CTAT current through a third resistor is configured to provide an output voltage greater than a silicon bandgap voltage.