# A 7.5-9 GHz GaAs Two-Channel Multi-Function Chip
## 3 Measurement Results  
Figure 7 shows the photograph of the two-channel multi-function chip which is fabricated by the 0.5 \(\upmu\)m GaAs E/D pHEMT process. The chip size is 3.5 mm \(\times\) 4.5 mm. On-wafer measurements  
Figure 5: (**a**) NO circuit structure, (**b**) NAND circuit structure, (**c**) D-flipflop circuit structure.  
Figure 6: The schematic of the digital circuit.  
are carried out for the performance characterization. A signal generator (NI-PXI) is employed to provide appropriate digital input waveform with a clock frequency of 10 MHz. The MFC is tested by vector network analyzer (Agilent PNA 5224A, Agilent Technologies Inc., Santa Clara, USA) using Ground-Signal-Ground (GSG) co-planar microwave probes pitch on probe station [12].  
Figure 8: _Cont._  
Figure 7: Photograph of the fabricated multi-function chip.  
As shown in Figure 9a,b, the input and output return losses of MFC are more than 19 dB in both channels. The attenuator and phase shifter exhibit good flatness of relative attenuation and relative phase shift, respectively, in the frequency range from 7.5 to 9 GHz (Figure 9c,d). In Figure 9e, measured root mean square (RMS) attenuation error of <0.45 dB and RMS parasitic phase error of <2.4\({}^{\circ}\) is shown at all 64 states. Figure 9f shows <2\({}^{\circ}\) RMS phase error and <0.2 dB RMS parasitic amplitude error measured for the phase shifter. The trend of measured results are almost in accord with simulated results for ATT and PHS. In Figure 9g, <13 dB insertion loss is achieved, and the difference between measured and simulated results may be caused by process model accuracy.  
Table 4 summarizes the performance comparison of this work with other published MFCs working in close frequency ranges. Characteristics including insertion loss, RMS phase error, RMS attenuation error, and return loss are better than the previous reported MFCs. This work is also integrated with two channels and a serial-to-parallel converter on a single MFC chip, which has the benefit of decreasing the system's size and cost. By applying new technologies like the 0.18 \(\upmu\)m GaAs E/D pHEMT process, the size of MFC could reach 4 \(\times\) 3.7 mm\({}^{2}\)[8]. However, comparing with the 0.5 \(\upmu\)m GaAs E/D pHEMT process, which is commonly used for the MFC designs in X-band, the cost of the 0.18 \(\upmu\)m process is much larger. Compared with other published MFCs with the same 0.5 \(\upmu\)m process, our design shows higher integration, the size of which is much smaller than the average 4 \(\times\) 5 mm\({}^{2}\)[13]. Furthermore, the 3.5 \(\times\) 4.5 mm\({}^{2}\) size of our MFC successfully approaches the above 4 \(\times\) 3.7 mm\({}^{2}\) fabricated by the  
Figure 9: (**a**) Measured channel 1 (CH1) input and output return loss of all states, (**b**) measured channel 2 (CH2) input and output return loss of all states, (**c**) measured relative attenuation of all states, (**d**) measured relative phase shift of all states, (**e**) measured and simulated CH1 and CH2 root mean square (RMS) error of attenuation and parasitic phases, (**f**) measured and simulated CH1 and CH2 RMS error of phase and parasitic amplitude, (**g**) measured and simulated CH1 and CH2 insertion loss.  
new 0.18 um technology. The frequency band 7.5-9 GHz of the MFC is chosen for a real application of narrow-band data transmission within 8-8.5 GHz.