# A Wideband High-Voltage Power Amplifier Post-Linearizer for Medical Ultrasound Transducers
## 3 Results and Discussion
### Experimental Performance Verification of the HVPA with Post-Linearizer
This is due to the IP\({}_{\rm 1 dB}\) for the HVPA (14.21 dB\({}_{\rm m}\)) being substantially lower than that for the HVPA with post-linearizer when 4 V and 5 V DC voltages were applied (18.86 dB\({}_{\rm m}\) and 18.35 dB\({}_{\rm m}\), respectively). Figure 6: (a) Gain and (b) gain deviation vs. input power of the HVPA without the post-linearizer (solid black lines) and HVPA with post-linearizer with 1 V and 2 V DC applied voltages (solid red lines and dash-dot blue lines, respectively); (c) Gain and (d) gain deviation vs. input power of the HVPA without the post-linearizer (solid black lines) and HVPA with post-linearizer with 4 and 5 V DC voltage applied (solid red lines and dash-dot blue lines, respectively). In accordance with the results from circuit design analysis (Equations (1) and (2)), the post-linearizer exhibited adequate capacity to operate efficiently over a wide input-power range when 4 V and 5 V DC voltages were applied. In Figure 6d, the gain deviation of the HVPA with post-linearizer when 4 V and 5 V DC voltages were applied (0.42 dB and 0.07 dB at 17 dBm input power, respectively) was lower than that of the HVPA without the linearizer (\(-1.23\) dB at 17 dBm). When 4 V and 5 V DC voltages were applied to the post-linearizer, the change in gain deviation of the HVPA with post-linearizer was from less than approximately 1 dB up to approximately 20 dBm input power. Additionally, the gain deviation values of the HVPA with post-linearizer were less than those of the HVPA without the post-linearizer up to 26 dBm input power. As also derived in Equation (2), we can conclude that the post-linearizer improves gain stability of the HVPA over a wide input power range because the post-linearizer circuit can offset the non-linearity of the input capacitances of transistor devices. Figure 7 illustrates the measured output power versus the input power when 10 MHz, 10-, 15-, 20-, 25-cycle pulse signals were applied to the HVPA with the post-linearizer in order to test for IP1 dB variances associated with higher input pulsed power. As shown in Figure 7, analysis of IP1 dB as a function of input power of the HVPA with post-linearizer when 1 V DC voltage was applied yielded the following results: 16.13 dBm, 16.17 dBm, 16.22 dBm, and 16.19 dBm, respectively. Analysis of IP1 dB as a function of input power of the HVPA with post-linearizer when 2 V DC voltage was applied yielded the following results: 16.50 dBm, 16.71 dBm, 16.71 dBm, and 16.75 dBm, respectively. Additionally, IP1 dB as a function of input power of the HVPA with post-linearizer when 4 V DC voltage was applied yielded the following results: 17.42 dBm, 17.32 dBm, 17.63 dBm, and 17.69 dBm, respectively. Lastly, analysis of IP1 dB as a function of input power of the HVPA with post-linearizer when 5 V DC voltage was applied yielded the following results: 18.31 dBm, 18.16 dBm, 18.23 dBm, and 18.28 dBm, respectively. The measured variances of the IP1 dB of the HVPA with the post-linearizer were less than 0.5 dBm, representing considerably low variances. Measured IP1 dB values of the HVPA with the post-linearizer under 1 V, 2 V, 3 V, 4 V and 5 V DC voltages were higher than that of the HVPA without the post-linearizer. Moreover, the measured IP1 dB values of the HVPA with the post-linearizer under 4 V and 5 V DC voltages were higher than that of the HVPA without the post-linearizer when the same DC voltages were applied. From this analysis, we can confirm that the IP1 dB of the HVPA with post-linearizer under higher DC voltages (4 V and 5 V) continued to yield improved efficiency compared to the HVPA without the post-linearizer. Figure 8 shows the measured gain and gain deviation as a function of frequency of the HVPA with and without the post-linearizer, respectively because the harmonic technique may be implemented with the 10 MHz ultrasonic transducer.