Performance of Double-Pole Four-Throw Double-Gate RF CMOS Switch in 45-nm Technology ()
1. Introduction
In the radio transceiver the switches, traditional n-MOS switch has better performance compare to PIN diodes (use of PIN diodes consumes more power), but only for a single operating frequency [1,2]. For multiple operating frequencies, high signal distortions are easily observed, which results in an unrecognizable information signal at the receiver end which would be measured by using the curve of capacitance and voltage with VEE Pro software [3,4]. A continuous scaling of CMOS technology has a better performance of both frequency and noise, where it is becoming a rigorous part for RF applications in the GHz frequency regime of the spectrum. The aggressive scaling of metal-oxide-semiconductor field effect transistors (MOSFET) has led to the fabrication of high performance MOSFETs with a cut-off frequency (fT) of more than 150 GHz [5]. As a result of this development, the CMOS is a strong candidate for the RF wireless communications in this frequency regime of the specrum.
For the Multiple-Input, Multiple Output systems, it is essential to design a new RF switch that is capable of operating with multiple antennas and frequencies as well as minimizing signal distortion and power consumption [6-8]. The excellent improvement in the frequency response of Si-CMOS devices has aggravated their use in the millimeter-wave regime such as high capacity wireless local area network, short range high data rate wireless personal area networks, and collision avoidance radar for automobiles. Using Si-CMOS for these applications allows for higher levels of integration and lower cost with improving the efficiency. Since for 65-nm technology has application of 60 GHz power amplifier designs [9,10], but recently few research group has demonstrated 60 GHz power amplifiers in 45-nm technologies.
For radio-frequency applications, generally, the common drive requirements for off-chip loads are of 50 Ω impedances. This impedance is a good compromise between lowest loss and highest power handling for a given cable size. Also this impedance caught on for RF transmission sooner than the well established 75 Ω that had been used for video transmission. The nodal capacitance, drain and source sidewall capacitances are the factors which controls the bandwidth of RF switches [11,12]. Since these switches are to be used with digital and baseband analog systems, control by on-chip digital and analog signals is another factor in the design [13].
In the design of DP4T DG RF CMOS switch structures with 45-nm technology for digital and analog, a transaction between speed and frequency response and circuit complexity is always encountered. The properties for RF CMOS switch design for the application in communication and designed results are presented and have been designed to optimize for the particular application [14]. A DP4T DG RF CMOS switch has the properties as fixed tuned matching networks, low quality factor matching networks, high power output, mounting flange packages, and silicon grease. Some bipolar RF CMOS transistors are suitable for automotive, commercial or general industrial applications.
In this paper, we present a comprehensive study of the RF switch performance of 45-nm low-power, high-speed double-pole four-throw double-gate radio-frequency complementary-metal-oxide-semiconductor (DP4T DG RF CMOS) switch. The DP4T DG RF CMOS switch structures with different aspect ratios for 45-nm technology and their layouts are studied to understand the effect of device geometry on working of switching properties. In this design transistor width increases for double-gate MOSFET such that peak power-added efficiency (PAE) and output power Pout decrease as these parameters decreases with increasing device width because of a reduction in fmax [15]. In a RF power amplifier, PAE is defined as the ratio of the difference of the output and input signal power to the DC power consumed. The RF power performance of 45-nm devices is shown to be very comparable to that of 65-nm devices.
An application for a CMOS switch covers the areas of micro power circuits and other wireless applications at frequencies from as low as 0.1 GHz for low earth orbiting satellite system to thousand of GHz [16]. Various circuit parameters have been discussed in this paper for better performance.
Each of the parameters will be discussed separately for the purpose of clarity of presentation and understanding the operation of DP4T DG RF CMOS switch structures for 45-nm technology. The organization of the paper is as follows; DP4T DG RF CMOS switch model is presented in Section 2, Characteristics of DP4T DG RF CMOS switch for layout are discussed in Section 3. The capacitances, Inductances and other parameters present in DG MOSFET for high speed RF switches are discussed in Section 4. The effective resistance of DP4T DG RF CMOS present in switch is discussed in Section 5. Finally, conclusion of the work is in Section 6.
2. DP4T DG RF CMOS Switch Model
The selections of RF CMOS switch require an analysis of performance specifications. Since drain-source breakdown voltage is the maximum drain-source voltage before breakdown with the gate grounded [17], also specifications for RF CMOS transistors includes the maxi-
Figure 1. DP4T RF CMOS switch with inverter property [14].
mum drain saturation, common-source forward transconductance, operating frequency, and output power. Devices that operate in depletion mode can increase or decrease their channels by an appropriate gate voltage. By distinction, devices that operate in enhancement mode can only increase their channels by an appropriate gate voltage. RF MOSFET transistors vary in terms of operating mode, packaging, and packing methods.
This paper proposes a design of DP4T DG RF CMOS switch structures at 45-nm technology for low power consumption and low distortion application of RF switch in communication that operates at 0.1 GHz to 60 GHz. The n-channel devices were used in the HF portion of the circuits with p-channel devices used as current sources. The switches which were designed to drive 50 Ω resistive loads and utilized multiple gate fingers to reduce parasitic capacitance is in an effort to improve the operating frequency [13].
The objective of proposed design of a switch is to operate at 0.1 GHz to few GHz frequency range for MIMO systems. This switch must mitigate attenuation of passing signals and exhibit high isolation to avoid corruption of simultaneously received signals [14]. According to the previous work, DP4T switch is a fundamental switch for MIMO applications because parallel data streams can be transmitted or received simultaneously using the multiple antennas. For instance, the transmitted signal from Power Amplifier (PA) is sent transmitter ‘A’ which is shown in Figure 1 with named as ‘A_Tx’ port and travel to the ANT1 node while the received signal will travel from the ANT2 node to the receiver ‘B’ with a named as ‘B_Rx’ port and pass onto the Low Noise Amplifier or any other application.
The proposed switch contains CMOS in its architecture and needs only two control lines (V1, V2) of 1.2 V to control the signal traffic between two antennas and four ports as shown in Figure 1, hence, improving port isolation performance two times, compared to the DPDT switch and reducing signal distortion. In addition, signal fading effects can be reduced because sending identical signals through multiple antennas will most likely result in a high quality combined signal at the receiver end. For the design of DP4T DG RF CMOS switch, we design a
Figure 3. Proposed DP4T DG RF CMOS switch.
double-gate as shown in Figure 2. This shows the double-gate n-MOSFET. Similarly, we can design doublegate p-MOSFET. Now, we convert the Figure 1, DP4T switch using the basic double-gate transistor as shown in Figure 2, for DP4T DG RF CMOS switch as shown in Figure 3.
Since in the Figure 1, four transistors are used for two antennas. In this antenna using the CMOS functionalityat a time any one of transistor M1 or M3 will operate and in the same fashion any one of transistor M2 or M4 will operate. Same function is measured in the proposed DP4T DG RF CMOS switch as in Figure 3. This circuit is designed with a Micro-Cap evaluation 6.0 tool. We can find easily that CMOS based RF switches allow longer battery life than PIN diodes, because current consumption is significantly reduced and also about 60 percent smaller than the smallest GaAs RF switch on the market. Furthermore, our switch also experiences minimal distortion, negligible voltage fluctuation, and low power supply of only 1.2 V. In this switch with compare to Figure 1, for A_Tx and B_Tx, two p-MOS are designed for parallel combination and for A_Rx and B_Rx, two n-MOS are designed for parallel combination which is better selection.
3. Characteristics of DP4T DG RF CMOS Switch for Layout
Figure 4 shows the layout of DP4T DG RF CMOS switch with two input voltages (Vin1 and Vin2) and output through antennas (ANT1 and ANT2) with two transmitters (Tx_A and Tx_B) and two receivers (Rx_A and Rx_B). This layout is drawn with Microwind 3.0 version tool. Here color code has their usual meanings [18,19]. Figure 5 shows the antenna voltages ANT1 and ANT2 with input voltages Vin1 and Vin2 for this transceiver switch. Drain current for this transceiver switch with output voltage is shown in Figure 6, which gives the drain current Idd (max) 0.387 mA, Idd (avg) 0.02 mA, also raise time 36 ps at 1 GHz operating frequency.