High Accuracy Tracking (HAT)
High Accuracy Tracking (HAT) is Nujira's patented architecture for Envelope Tracking power supply modulators.
The HAT topology combines high efficiency Switch Mode Power Supply (SMPS) technology with a high bandwidth linear Error Amplifier, to achieve a highly agile ET power supply.
Key features of the HAT architecture are:
- High Bandwidth
- Low Noise
- High Efficiency
- "Buck-Boost" capability
To accurately track the envelope of an RF signal requires a power supply bandwidth of 2x-3x the instantaneous RF channel bandwidth. For example, a supply bandwidth of 40-60 MHz is required to track a 20 MHz LTE RF channel.
The HAT topology uses a high bandwidth linear Error Amplifier, which can provide tracking bandwidths extending to 100 MHz and beyond.
To achieve the same bandwidth from a conventional SMPS technology would require switching frequencies of 500-600 MHz or more - even if this switching frequency could be achieved, switching losses would result in a significant loss of efficiency.
An Envelope Tracking PA does not have any supply decoupling capacitors, relying instead on the low impedance active supply from the ET modulator. Any noise on the power supply appears on the RF output of the PA, requiring an exceptionally low noise design for the ET modulator.
Nujira's HAT architecture uses the linear Error Amplifier to remove any SMPS transient noise from the signal, resulting in products which deliver high efficiency without compromising on noise performance.
One of the main challenges with ET modulator design is to achieve a high power supply conversion efficiency, otherwise all the benefit gained in the PA may be lost as dissipation in the ET modulator. Maintaining high efficiency as bandwidth increases is particularly challenging.
Just as hi-fi loudspeakers combine "woofers" and "tweeters" to provide high quality over a wide frequency range, the HAT architecture uses a SMPS to deliver most of the power to the PA, with high efficiency but a relatively low bandwidth.
The high bandwidth linear Error Amplifier then adds the higher frequency components, which contain much less energy, resulting in highly accurate tracking of the input waveform up to 30-60 MHz and beyond.
By careful design of the ET modulator, Nujira's HAT architecture typically provides supply conversion efficiencies of 80% and beyond, even for high bandwidth signals like LTE.