2.4 GHZ HETERODYNE RECEIVER FOR HEALTHCARE APPLICATION

Methods: In the first part, a low noise amplifier (LNA), which is commonly used as the first stage of a receiver, is introduced and simulated. LNA performance greatly affects the overall receiver performance. The LNA was designed at the 2.4 GHz ISM band, using the cascode with an inductive degeneration topology. The second part of this proposal presents a low power 2.4 GHz down conversion Gilbert Cell mixer. In the third part, a highperformance LC-tank CMOS VCO was designed at 2.4 GHz. The design uses using PMOS cross-coupled topology with the varactor for wider tuning range topology.

Currently, remote monitoring applications are extremely important mobile technologies, because they can detect and prevent the illness. Thus, they could reduce hospital readmission rates, saving hospital resources. Remote monitoring systems help patients effectively be aware of their physical conditions, and commute more efficiently get in touch with their physicians [1]. Fig. 1 shows that the basic sensing unit can collect physiological signals (e. g.: such as EEG, ECG, body temperature, pressure etc.), blood when individual sensors are attached to the human body [2]. The processing unit processes all the sensed signals, then processes all the data based on the communication protocols. All the processed data will be transmitted through a wireless link to a portable personal base-station.

Fig. 1: Block diagram of a typical sensor node
The main challenge of such remote monitoring systems is the high power consumption of portable devices. A solution to this challenge is the integration of the portable devices' digital part and the RF part onto one chip.
When the transmitter sends out the data, the receiver will pick up the signal and will perform DSP processing [2]. The requirement of this transmitter and receiver is that both should have low power. For the front-end receiver, the major objectives are 1) receiving the RF signals and 2) recovering the biosignal classification. This paper proposes a low power receiver design. This system can be used in wireless ECG acquisition systems. In order to meet the standards, the system is designed as shown in table 1. The objective of this research is to build a 2.4 GHz Heterodyne receiver, which consists of an LNA, a mixer and a VCO.
In this proposal, LNAs use cascode inductor degeneration topology, mixers use gilbert cells, and VCOs use LC tank topologies. All of these components use 2.4 GHz. First, the LNA has a cascode topology and an input matching network with a series inductor to achieve a high gain of the LNA. This is shown by our simulation, which consumes only 1.7 mA with a 1.3 V power supply and achieves a gain of 20 dB and NF of 1.9 dB.

Fig. 2: 2.4GHz LNA design schematic design
Second, the mixer is a double balanced active mixer using gilbert cell topology, which has a high conservation gain.  In fig. 2, there is a cascode common-source with inductive degeneration [4]. The M1 and M2 consisted of cascode opamp and the tank circuit consisted of by Cd and Ld. The transistor M3 was used for amplifier biasing. The purpose of inductors Lg, Ls and capacitor Cgs was to match to the 50Ωinput. The degeneration inductor Ls had better linearity at the cost of lower gain for linearity. Rs was used to isolate the RF biasing signals. Other capacitors were used to block DC signals.
As seen in fig. 3 (a), the gain is 15. As seen in fig. 3(b), the NF in is around 1.9 dB at 2.4 GHz, and that the major contribution of the noise is from M1 and Ls, also, the total power of the LNA is 2.2 mW.
As seen in fig.4, the frequency is at 2.4 GHz the S11 is less than-10 dB. Kf is larger than 1 for all frequencies from 1 to 5 GHz, so this circuit is totally stable. Gilbert mixer, as seen in fig. 5 (a), provides good port-to-port isolation with some conversion gain [4]. The M1 and M2 are the input stages operating in the saturation region.
LO signals need to make the M3, M4, M5 and M6 transistors full switch, which means which transistor M3 M5 and M4 M6 are turning on alternately. In other words, LO signals must be kept at an appropriate large magnitude to ensure transistors switching accurately. Linearity is the greatly contributed decided by the transconductance stage.
The transistors components values can be seen in table 3. As seen fig. 5 (b), based on the PSS simulation, the conversion gain VS RF power at 2.4 GHz is 14.6 dB. Also, NF is 15dB while the power consumption is 8.2 mW.
The VCO schematic as shown in fig. 6 (a) was chosen for several reasons. The PMOS pair determines the oscillation amplitude of this structure, which would also be beneficial to the low phase noise.
The cross-coupled MOS pair would get a negative resistance as shown in fig.6 (a). The negative resistance cancels the LC element's parasitic resistance [6]. The transistor value can be seen in table 4.  The oscillation frequency is around 2.4 GHz. As we can see fig.6 (b) phase noise at 1 MHz offset frequency is 129 dBc/Hz, the major noise source is the current source and the two differential pair. For simulation results at [7].
In hospital healthcare, the monitoring system can help doctors to monitor the patient's physiological parameters. Using proposed technology, a pregnant woman can be checked for such parameters as Blood Pressure (BP) and heart rate of the woman and heart rate and movements of fetal to control their health condition. In her proposed system, a coordinator node can be attached to a patient's body to collect all the signals from the wireless sensors and sends them to the base station. The attached sensors on a patient's body form a wireless body sensor network and they are able to sense the heart rate, blood pressure and so on. The main advantage of this system in comparison to previous systems is to reduce the energy consumption to prolong the network lifetime, speed up and extend the communication coverage to increase the freedom for enhance patient quality of life. Patients can reduce the cost of staying hospital, and doctors can monitor patients' conditions at any time. Thus, poor people can receive better healthcare, and do not have to worry about money.