As the data transmission rate of cellular networks increases, the demand for data transmission by data cards and mobile phones is also increasing. As far as WCDMA mobile phone amplifiers are concerned, since mobile phones are often used in dense urban areas of base stations, efficient operation is required in the medium and low output power range; on the other hand, for data transmission, the increase in transmission volume leads to PAs. Work more in high output power mode. For data cards and mobile phones, high efficiency is more important for data cards. Therefore, in addition to providing power amplifiers for mobile phones, many power amplifier manufacturers also develop power amplifiers for data cards or high-speed data transmission. Mitsubishi Electric has developed a high-efficiency power amplifier "BA012Fx" for data transmission, which has been released recently. This article mainly introduces the design concept and experimental results of the BA012Fx series. This article refers to the address: http:// New power amplifier for data card based on GaAs HBT process GaAs HBT (GaAs Gallium Heterojunction Bipolar Transistor) amplifiers are widely used in the field of CDMA mobile phones. This is because HBT has a higher output power density than FETs, and HBT can be driven by one bias voltage. Therefore, HBT power amplifiers have been developed in the field of mobile phones for many years. Mitsubishi Electric has developed the BA012Fx series of power amplifiers for data cards. The series has five frequency bands, namely Band1 (1920MHz~1980MHz), Band2 (1850MHz~1910MHz), Band3 (1710MHz~1785MHz), Band5 (824MHz~849MHz), Band8. (880MHz~915MHz), suitable for WCDMA networks in Asia, North America, Europe and Japan. Figure 1 shows the appearance of the BA012Fx series of power amplifier modules, measuring 3mm * 3mm * 1mm. With a maximum output power of 670mW (28.25dBm) and a power added efficiency (PAE) of 45%, it has the highest level of performance in its class. The amplifiers are integrated internally with (i) attenuators: to change the gain of the amplifier and to reduce the signal-to-noise ratio at low input power; (ii) coupler: for detecting output power. We also added phase control to the attenuation circuit to reduce phase error when changing gain. Figure 1 The BA012Fx series amplifiers are only 3mm*3mm*1mm. At present, mobile phone power amplifiers usually use switching channels to improve performance at low and medium output power. However, the loss of the switching circuit itself that provides the path switching function reduces the power added efficiency (PAE) of the entire power amplifier. Therefore, the BA012Fx series power amplifier does not use any switching circuit on the final output path, thereby achieving high power added efficiency at high output power. Figure 2 is a block diagram of the data card amplifier. The power amplifier module consists of a two-stage amplifier and an attenuator between the primary amplifier and the secondary amplifier. Such a structure can reduce the noise figure in the low gain mode. The use of a BiFET (Bipolar Field Effect Transistor) as an attenuator is to reduce the size of the chip because a FET switch circuit can be provided on the same chip. Therefore, the chip size is smaller than that of a switching circuit using a bipolar transistor. Three-dimensional electromagnetic analysis is used to make the line layout more reasonable. A single step attenuation circuit is used, as shown in Figure 3. In high gain mode, SW1 of the FET is turned on and SW2 is turned off; the RF signal can pass directly, and the loss is minimal. In low gain mode, SW1 of the FET turns off SW2, and the signal loses 14dB after passing through the series and shunt resistors. In order to compensate for the phase change of the attenuator during switching, a series capacitor C1 is added. Figure 2: Block diagram of the power amplifier architecture. Figure 3: Attenuator circuit diagram. Performance test result Based on the above design description, we tested the performance of Mitsubishi Electric BA012F5 (WCDMA Band 5). The modulation signal is WCDMA (3GPP-R99) and the applied bias voltage is 3.4V. Figure 4 shows the S-parameter measurements of the amplifier. The gain step is 13dB, and when the attenuator is turned on, the phase changes ≤10°. The input reflection loss (S11) in both modes is less than -10dBc. Figure 4: S-parameter measurements of the amplifier. Figure 5 shows the relationship between ACLR and output power level. The amplifier has a maximum output power of 28.25dBm, a linear gain of 27dB, a PAE of 45%, and an ACLR of -40dB. Compared with traditional power amplifiers, PAE has increased by about 5%. Figure 5: Relationship between ACLR and output power level. Figure 6 shows the performance of the coupler (VSWR2.5:1). The coupling coefficient changes less than 0.6 dB. The BA012Fx series is designed for Band1, Band2, Band3, Band5 and Band8. All amplifiers in the BA012Fx series meet PAE=45% and ACLR=-40dBc. Figure 6: Coupler Performance (VSWR2.5:1) Summary of this article We tested the BA012Fx series of power amplifiers dedicated to data cards from Mitsubishi Electric. This paper introduces its circuit and performance. This series of amplifiers uses a single-step attenuation circuit to control the gain, and a phase compensation circuit to optimize the phase change when the gain changes. Achieved the highest level of power-added efficiency of 45%, which is about 5% higher than traditional power amplifiers. Figure 7: Block diagram of the power amplifier architecture for mobile phones and data cards.
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