30W Ericsson Classic Balanced Amplifier: Driver + End-Level Pure Balanced Architecture, How Does IP3 Actually Perform?

ERICSSON AB: The official logo of Ericsson (Swedish headquarters).TVA 117 3560: This isBoard model / material number（Part Number）。TVAThe series is usually Ericsson base stationsRF amplifier module.

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4-stage amplifier

Signal flow:
After passing through a DC-isolated capacitor, the SMA connector input signal is marked with silkscreenXT2The amplifier performs the first stage of amplification; Then it passesAV113The variable attenuator controls the gain, then splits into two channels via an orthogonal hybrid coupler (90° balanced split), each consisting of two stagesXT2The amplifier amplifies the stage, and finally the combined output drives the power amplifier stage.

Shielding Structure Edge Structure:The edges of the boards are densely packedGrounding via + shielded padDesign, forming a complete structureFaraday shielding cageEdge. The goal is to minimize RF signal leakage and external interference.

EMC: 2 groupsEMC filter components(Capacitors, inductors, or ferrite beads). Used for filtering power or control lines, suppressing electromagnetic interference (EMI), meeting the strict EMC standards of base stations.

Adjustable capacitors(Middle arrow): Used in RF matching networksFine-tune impedance matching, used during factory production or maintenance to optimize VSWR and output power/linearity.

Why do RF and power wiring both use right-angle turning?

In modern high-speed/high-frequency PCB designs, right-angle traces are usually avoided (45° beveled or arc transitions are recommended) to reduce impedance abrupt changes and signal reflections. However, this early Ericsson 3G base station amplifier board (TVA 117 3560) extensively uses right-angle cable routing for the following reasons:

Design advantages：Mature processes and lower costs; By precisely combining line width and right angles, the required 50Ω characteristic impedance can be achieved in the 2110-2170 MHz band, and the parasitic effects of right angles can be controlled or even utilized by design in this band; At the same time, right-angle routing makes the layout more compact, facilitating the layout of high-density RF amplifiers, and also facilitating uniform and consistent etching during mass production. Using right-angle power wiring facilitates decoupling capacitor layout and shortens the current circuit.

Potential impact：Right angles introduce certain impedance discontinuities and parasitic parameters, but the impact is controllable in the 2.1 GHz band. Combined with dense ground vias and shielding designs, overall performance remains reliable.

Intermediate drive stage.

Infineon (formerly Ericsson) PTF102015Product datasheet, showcasing a product specifically designed for you2110-2170 MHz WCDMABase station design30W GOLDMOS LDMOS Power MOSFET, with a typical gain of 13-14dB and an efficiency of 47%, featuring full gold metallization, high reliability, integrated protection, and good linearity (ACPR), suitable for use in the final stage or driver stage of older Ericsson base station amplifiers.

2 PTF102015(Infineon LDMOS FET) Each unit is rated for each piece30W, When two units are connected in parallel/balanced, the total output power can reach60WLeft and right (in practical applications, affected by heat dissipation, bias, and linearity requirements, often operating within the 30-50W range). Structural features:

Input/output uses an orthogonal hybrid coupler (90° Hybrid)Achieve power distribution and synthesis (yellow matching network + traces in the image).

50Ω power load: The symmetrical structure on both sides contains 50Ω load resistor(or isolation resistors), used to absorb unbalanced power and reflections, improving port isolation and stability.

Matching networks: Each power transistor has a complex microstrip + capacitor matching circuit before and after (marked as "matching?" in the diagram). "Region), used to achieve input/output impedance transformation up to 50Ω.

Right-angle alignment:RF signal paths make extensive use of right angles, combined with precise linewidth control to achieve characteristic impedance matching (as previously analyzed).

Advantages:

The balanced structure allowsLinearity (IP3) is better、Port VSWR is low, and graceful degradation remains when a single transistor fails.

Suitable for communication systems requiring high linearity, such as WCDMA.

This is typicalHigh-power RF final stage design, high reliability and mature debugging, making it a classic solution for Ericsson's old base station amplifiers.

This Ericsson base station amplifier board (TVA 117 3560) has a silkscreen labelXT2What model of amplifier is the device?From the board, XT2 appears in multiple places; it should be a driver stage or preamplifier, packaged in SOT-89 or similar surface-mount packages. Does anyone know the specific model (or datasheet)? Thank you very much!

For details, see the previous section: Theoretical principles 👇 of balanced amplification structures.