# A 2.4 GHz 20 W 8-Channel RF Source Module with Improved Channel Output Balance
## 2 Materials and Methods
### RF Source Generation/DC Control Part  
The RF source generation/DC control part provides DC bias to ensure the safe operation of the proposed RF source module and generates an initial RF source delivered to the power amplification part. At the first step, a voltage-controlled oscillator (VCO),  
Figure 1: Block diagram of the proposed RF source module.  
CVCO55 CC-2328-2536 (Crystek Corporation, Fort Myers, USA) generates an initial RF source that has a specific frequency controlled by the DC control voltage without a signal generator. Then, a voltage gain amplifier (VGA), MAX205/ETX+ (Maxim Integrated, San Jose, USA), is used to provide insufficient gain between the VCO and source PA. This is also tuned by the DC control voltage. To control the frequency of the VCO and the gain of the VGA, trimmer resistors, 3214W-1-204E (Bourns, Altadena, USA), are used. Subsequently, the source PA, ACPM-5040 (Avago Technologies, San Jose, USA), amplifies the delivered power from the VGA up to 30 dBm to transmit it to the power amplification part. The DC bias of the source PA uses VSRC_EN = 2.6 V and VSRC_CC = 5 V.  
Six external DC biases are required to operate the proposed RF source module, as shown in Table 1. The module requires 30 V of the main DC bias, called VSUPLY. The rest of the DC bias is used as the control bit for the proposed module operation as described in Table 2. This is because it prevents the drive and main PAs from burning out through sequential on/off. Gallium nitride high electron mobility transistor (GaN HEMT) devices normally have an on-state characteristic. If a drain bias is applied without closing the drain-source channel, excessive current flows through the channel, causing damage to the transistor. The process of turning off is in the reverse order of the operating sequence. A solid-state relay (SSR), CMX60D20 (Crydom, Mansfield, USA), supplies a drain bias for the drive and main PAs. The other relays, 8L01-05-111 (Coto Technology, North Kingstown, RI, USA) for SPST and 8L61-05-111 (Coto Technology, North Kingstown, USA) for SPDT, act as switches to turn the other active devices on or off. A negative charge pump, MAX868 EUB (Maxim Integrated, San Jose, USA), generates a negative DC bias to maintain the off state of the drive and main PAs. Low dropout regulators (LDOs), TPS54560 DDAR (Texas Instruments, Dallas, USA) and TPS7A7001 DDAR (Texas Instruments, Dallas, USA), convert high-level voltage to low-level voltage to supply the proper DC bias to the components. A printed circuit board (PCB) for the RF source generation/DC control part was designed on 4-layer FR-4.  
\begin{table}
\begin{tabular}{c c c} \hline
**DC bias** & **DC Level** & **Description** \\ \hline VSUPLY & 30 V & Main DC source \\ VSR\_CTRL & & Control bit for the drain bias of the drive and main PAs \\ VMA\_CTRL & high (5 V) & Control bit for the main PAs on/off \\ VDF\_VDF\_CTRL & or & Control bit for the drive PA on/off \\ VSR\_CTRL & low (0 V) & Control bit for the source PA on/off \\ VRF\_CTRL & & Control bit for the VCO and the VGA on/off \\ \hline \end{tabular}
\end{table}
Table 1: Description of the external DC biases.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sequence** & **VSSR\_CTRL** & **VMAIN\_CTRL** & **VDRV\_CTRL** & **VSRC\_CTRL** & **VRF\_CTRL** & **Description** \\ \hline
1 & L & L & L & L & L & off state \\
2 & H & L & L & L & L & ideal state \#1 \\
3 & H & H & H & L & L & ideal state \#2 \\
4 & H & H & H & H & H & power \\  & & & & & & emission \\ \hline \end{tabular}
\end{table}
Table 2: Operating sequence for the proposed RF source module.  
* Sequence 3 (ideal state #2): When V\({}_{\text{MAIN\_CTRL}}\) and V\({}_{\text{DRV\_CTRL}}\) become high, the gate bias of the drive and main PAs is changed from -5 V to -2.7 V to activate these components.
* Sequence 4 (power emission): When V\({}_{\text{SRC\_CTRL}}\) and V\({}_{\text{RF\_CTRL}}\) become high, the proposed RF source module generates 20 W output power at each channel.