Low Modulation Bandwidth Envelope Tracking Circuit Offset Control
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Solution Overview
Problem
Existing envelope tracking (ET) circuits struggle to maintain an ET modulated voltage at a peak level for a sufficient duration when amplifying lower modulation bandwidth RF signals, particularly in IoT networks, due to discharge of the offset capacitor and insufficient battery voltage, leading to reduced power amplification efficiency and increased error vector magnitude (EVM).
Innovation Solution
A low modulation bandwidth (LMB) ET circuit is designed with an amplifier and an offset circuit that generates a modulated offset voltage proportional to the target voltage, allowing the ET modulated voltage to be maintained at a defined level for a defined duration by using an offset capacitor and control circuitry to prevent discharging, ensuring efficient amplification of RF signals to a defined power level in IoT networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If an existing ET circuit is used to amplify lower modulation bandwidth RF signals, then the circuit can operate with standard components, but the ET modulated voltage cannot be maintained at peak level for sufficient duration due to offset capacitor discharge
Solution Approach 1:
The control circuit proactively detects when the offset capacitor voltage drops below a threshold and immediately activates the charge pump to recharge it, preventing the voltage drop from affecting amplification performance. This preliminary action ensures the ET modulated voltage maintains peak level for the required duration.
Solution Approach 2:
The control circuit continuously monitors the offset capacitor voltage and uses this feedback to control the charge pump operation. When voltage drops below threshold, the charge pump activates; when voltage reaches target level, the charge pump stops. This closed-loop feedback ensures reliable voltage maintenance.
2Reliability
If battery voltage is increased to maintain ET modulated voltage at peak level, then sufficient voltage headroom is available, but power consumption increases and device size grows
Solution Approach 1:
Instead of using a high-voltage battery continuously, the system uses periodic charge pump activation to maintain offset capacitor voltage. The charge pump operates only when needed (when voltage drops below threshold), consuming minimal energy while ensuring sufficient voltage headroom during amplification.
Solution Approach 2:
The offset capacitor serves itself by maintaining voltage through periodic self-charging via the charge pump controlled by the control circuit. This eliminates the need for a higher-voltage battery, reducing power consumption while maintaining reliable voltage headroom when needed.
3Device complexity
If a simple ET circuit without offset control is used, then device complexity is reduced, but the ET modulated voltage duration is insufficient for LMB RF signals
Solution Approach 1:
The control circuit acts as an intermediary between the offset capacitor and charge pump, adding minimal complexity while enabling precise voltage management. This intermediary component coordinates the charge pump activation to extend voltage maintenance duration without requiring major circuit redesign.
Solution Approach 2:
The system dynamically adjusts the offset capacitor voltage parameter through controlled charging cycles. By changing the voltage parameter actively rather than relying on fixed high battery voltage, the system extends duration while keeping circuit complexity low.
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 LMB ET circuit effectively prolongs the duration of the ET modulated voltage at a peak level, enabling efficient amplification of LMB RF signals to a defined power level, such as 26 dBm, without compromising EVM, even with lower battery voltages, thus enhancing the performance in IoT networks.
Implementation Method 1
using an offset capacitor and control circuitry to prevent discharging
Implementation Method 2
an amplifier configured to generate a modulated amplifier voltage at an amplifier output based on the modulated target voltage
Implementation Method 3
The offset circuit is also configured to cause a modulated offset voltage being generated between the amplifier output and the output node based on the modulated target offset voltage
Data Source
AI summary
A low modulation bandwidth (LMB) envelope tracking (ET) circuit is provided. The LMB ET circuit is configured to generate an ET modulated voltage at an output node based on a modulated target voltage for amplifying an LMB radio frequency (RF) signal. More specifically, the LMB ET circuit includes an amplifier configured to generate a modulated amplifier voltage based on the modulated target voltage and an offset circuit configured to raise the modulated amplifier voltage by a modulated offset voltage at the output node. The offset circuit is configured to generate the modulated offset voltage based on a modulated target offset voltage that is proportional to the modulated target voltage. As a result, it may be possible to maintain the ET modulated voltage at a defined voltage level for a defined duration such that the LMB RF signal can be amplified to a defined power level.