How to solve the heating problem of diodes in communication circuits?

1, The heating mechanism of diodes in communication scenarios
The particularity of communication circuits leads to three main characteristics of diode heating: high-frequency switching loss, reverse recovery loss, and parasitic parameter loss. Taking the 5G base station PA module as an example, its operating frequency has exceeded 4GHz, and the diode needs to complete the conduction cutoff switching within nanoseconds. At this point, although the reverse recovery time (trr) of traditional fast recovery diodes (FRDs) has been optimized to 20-50ns, significant losses still occur under high-frequency switching. According to Joule's law, when the switching frequency increases from 1MHz to 10MHz, the switching loss of the diode will increase exponentially.
Reverse recovery loss is another major heat source. When the diode switches from the conducting state to the cutoff state, the minority carriers stored in the PN junction need to be eliminated through recombination or extraction, and the reverse recovery current (Irr) formed by this process can reach 1.5-3 times that of the forward current. In the DC-DC conversion circuit of communication power supply, if a fast recovery diode with trr=35ns and Irr=2A is selected, the reverse recovery loss of a single tube can reach 0.7W at a switching frequency of 1MHz, directly leading to an increase in junction temperature.
The parasitic parameter loss originates from the packaged inductance (Lpar) and lead resistance (Rlead). In millimeter wave communication (24-100GHz) scenarios, a parasitic inductance of 0.5nH can generate an overshoot voltage of 5V when a current of 10A changes, causing additional power consumption. A certain satellite communication equipment once experienced module thermal failure due to an unoptimized diode lead resistance, resulting in an increase of 0.3W in single tube power consumption.
2, Special challenges of communication circuits
Communication equipment imposes four strict requirements on diodes:
High frequency compatibility: 5G base stations require components to support the 0.3-6GHz frequency band, and the cutoff frequency (fT) of traditional Si diodes is only 100-300MHz, which is difficult to meet the requirements.
Low loss characteristic: The optical communication module requires a diode conduction voltage drop (Vf) of less than 0.3V to reduce signal attenuation.
High reliability standard: Aerospace communication requires components to operate stably within a temperature range of -55 ℃ to+125 ℃, with a failure rate (FIT) of less than 10 ^ -9/h.
Miniaturization requirement: The T/R module of phased array radar needs to integrate hundreds of diodes, and the size of a single component needs to be controlled within 0.5mm × 0.5mm.
A certain base station manufacturer once used traditional Schottky diodes (SBDs) for power synthesis, but due to the device trr=10ns, the efficiency decreased by 5%. Eventually, they switched to GaN HEMTs with ultrafast recovery diodes (UFRDs), which increased the system efficiency to 92%.
3, Systematic solution
(1) Device level optimization
Material Innovation: The third-generation semiconductor materials (GaN, SiC) have shown significant advantages. The electron mobility of GaN diodes is 5 times that of Si, with a cutoff frequency of up to 10GHz and a 70% reduction in on resistance (Rds (on)). After using SiC SBD on a certain satellite payload, it remained stable at a high temperature of 200 ℃ and reduced power consumption by 60%.
Structural innovation: Super Junction technology homogenizes the electric field distribution by alternately arranging P/N columns, reducing the Vf of 600V SiC SBD from 1.7V to 1.1V. Trench MOSFET structure reduces the on resistance from 2m Ω· cm ² in traditional planar structures to 0.5m Ω· cm ².
Process breakthrough: The use of ion implantation technology enables precise control of doping concentration, reducing the reverse recovery charge (Qrr) from 50nC to 5nC. A certain optical module manufacturer has shortened the response time of 10Gbps PIN diodes to 30ps by optimizing the thickness of the epitaxial layer.
(2) Circuit level design
Synchronous rectification technology: By replacing traditional diodes with N-type MOSFETs, the efficiency of 48V communication power supplies has been improved from 85% to 94%. After adopting this technology, a certain data center achieved an annual power savings of 1.2 million kWh.
Soft switching topology: LLC resonant converter achieves zero voltage switching (ZVS) through resonant current, reducing diode voltage stress by 40%. In a 5kW communication power supply, this topology achieves an efficiency breakthrough of 96% and reduces temperature rise by 15 ℃.
Layout optimization: 3D packaging technology is used to vertically integrate diodes with driver chips, reducing parasitic inductance from 3nH to 0.5nH. A certain 5G small base station optimized PCB routing to reduce diode loop inductance from 10nH to 2nH, reducing switch losses by 65%.
(3) System level thermal management
Phase change material (PCM): embedded with paraffin based PCM in diode packaging, utilizing its latent heat of melting (200-250J/g) to absorb peak heat. Experiments have shown that PCM can reduce the amplitude of junction temperature fluctuations by 40% at a heat flux density of 10W/cm ².
Microchannel cooling: Silicon based microchannel heat sinks are used in the AAU module of the base station, with a water cooling channel width of only 50 μ m and a convective heat transfer coefficient of 10 ^ 4W/(m ² · K). A certain operator's actual test shows that this technology reduces the temperature rise of diodes from 65 ℃ to 38 ℃.
Intelligent temperature control algorithm: By monitoring the changes in diode Vf in real time (Vf decreases by about 2mV for every 1 ℃ increase in temperature), dynamically adjusting the switching frequency and duty cycle. After adopting this algorithm, a certain optical transmission device can control the output power fluctuation within ± 0.5dB in an environment of -40 ℃ to+85 ℃.
4, Industry practice cases
Huawei has adopted a power synthesis scheme using GaN HEMT paired with SiC SBD in the design of 5G Massive MIMO antennas, which has increased the single channel output power from 40W to 64W with an efficiency of 48%. ZTE Corporation applies Trench MOSFET synchronous rectification technology in optical transmission modules, reducing the power consumption of 200G optical modules from 24W to 18W. Ericsson integrates microchannel cooling systems in base station power supplies, enabling power density to exceed 1kW/L and diode junction temperature to remain stable below 85 ℃.