Claims:The scope of the invention is defined by the following claims:

Claims:
1. Complex filter architecture using OTA to remove the image frequency problem is designed to achieve the following.
a) Complex notch filter is designed to shift the frequency to left side.
b) The frequency shifting is achieved using capacitor and transconductance Gm.
c) Filter can be used to remove negative frequency.
d) Filter is suitable for wireless Bluetooth applications.
2. As mentioned in claim 1, using four OTAs and capacitors, the architecture of the filter is used to shift the filter cut off frequency to the left side.
3. As mentioned in claim 1, the left side shifting is achieved by changing the value of capacitance and transconductance Gm of OTA.
4. As mentioned in claim 1, by connecting the complex notch filter at the output of low pass filter is used to remove the negative frequency response of the low pass filter.
5. As mentioned in claim 1, the complex notch filter with 4Ghz cutoff frequency is best suitable for wireless Bluetooth applications. , Description:Field of Invention
The present invention relates to, removal of image frequency in wireless receivers. The wireless receiver architectures need to have a complex filter or a polyphase filter after the IF stage to remove the unwanted signal frequency which is equal to the IF frequency. The complete frequency shift to remove the unwanted frequency is not possible by using the lower order filters. Higher order filters are preferred to get the complete frequency shift. The invention relates to the design of complex filter, which will remove the unwanted noise in the wireless receivers.
The objectives of this invention
The objective of this invention is designing of a complex notch filter using Operational Transconductance Amplifier (OTA) for removing image noise in wireless receivers.
Background of the invention
Nowadays, the design of front end wireless receiver place an important role in wireless communication is demanded. The wireless receivers are categorized as DCR (Direct Conversion Receivers) and super heterodyne receivers. DCRs are suffering with high flicker noise and the design of pre-sized DCR is also not a feasible solution. Moreover, the DCR technique is not suitable for bio-medical applications due to their low frequency band, i.e. limited to 10 Hz-3 KHz. Hence, most of the wireless receivers are using super heterodyne architecture, where radio frequencies are converted to IF (Intermediate Frequency) and IF again down converted to AF(Audio Frequency) (Hoshuyama, O. et. al, [1999], A robust adaptive beam former for microphone arrays with a blocking matrix using constrained adaptive filters). In receivers RF (Radio Frequency) is down converted to IF. In this process, the unwanted signal frequency which is equal to IF frequency also enters into the mixer. This unwanted signal frequency is called image frequency. The wireless receiver architectures need to have a complex filter or a poly phase filter after the IF stage to remove this unwanted signal frequency which is equal to the IF frequency. In order to suppress the image frequency in supper heterodyne receivers, very high Q value is required or more number of IF stages are required. The high Q value is possible with passive off-chip SAW (Surface Acoustic Wave) filters, which is not possible to fabricate on the chip.
Description of Prior Art
The other alternative techniques to overcome the image frequency problem are CMOS poly phase filters (Complex Filters), RC-CR filters, Opamp-C filters, Switched capacitor filters and OTA filters. However, the above stated filter architectures have the following disadvantages. The RC-CR filters are mostly passive in nature and occupy a large chip area. Because of low gain bandwidth product and low slew rate of Op-amp, the Opamp-C filters are valid for low frequency applications. Even though, the switched capacitor filters consume low power, but these filters suffer with flicker noise. All the above stated limitations are conquered by OTA-C filters, with high gain bandwidth product and high slew rate. Different types of CMOS OTA complex filter designs are available in the literature (Lin et.al,[2004], Analysis and improvement on propagation efficiency of high-speed asymmetric differential transmission system),( Devito, L.M. et.al,[1996], A versatile clock recovery architecture and monolithic implementation), but there is a tradeoff between the power and IRR. The high IRR consumes high power. A conventional complex band pass filter was made by shifting the negative cutoff frequency to the positive frequency of the low pass filter. In conventional GmC filters, the order of the filter should be very high to get the improved band pass filter response with high IRR. The high IRR consumes high power.
Summary of the invention
In the present innovative invention, is addressed the image frequency problem in wireless receivers Normally, negative frequency response or image frequency response of the low pass filter is shifted towards right using a complex filter. The complete frequency shift is not possible by using the lower order filters. Higher order filters are preferred to get the complete frequency shift. Instead of using the higher order filters, the asymmetric response of the lower order complex filter is connected with the asymmetric notch filter. This filter architecture has a cutoff frequency, which is very close to the second order conventional complex filter negative cutoff frequency. The resultant signal gives improved band pass response with a high IRR and improved Q factor with just a first order complex notch filter.
Detailed description of the invention
The complex notch filter is similar to complex band pass filter. In the proposed filter architecture, the high pass filter frequency response will be shifted by the amount of ?o to the left side of the origin. The low cutoff frequency high pass filter alone can be used in place of a complex notch filter. The design of GmC high pass filter with a very low cutoff frequency is difficult because of high capacitance and low Gm is required. The high pass filters lower cutoff frequency is proportional to Gm/C. In order to achieve lower cutoff frequency around 45 KHz need to have very high capacitance more than 100 pF, when Gm is tuned to 46 µs. High Gm can be achieved by increasing the bias tail current of OTA cell, even though the effective Gm value is not sufficient to get very low cutoff frequency. The complex stop band or notch filter is used to get the desired cutoff frequency. With the proposed complex notch filter, the positive notch frequency is shifted to the left side as mentioned earlier.
The proposed complex notch filter shown in Fig. 1 and the value of the capacitance decreases the notch shifting the frequency towards left side will also increase The desired notch response can be achieved by tuning the capacitance C connected in the circuit with a fixed value of Gm. The high pass filters cutoff frequency is shifted towards the left side by a frequency ?o. The frequency transformation from the high pass filter to the complex band reject filter is expressed in Eqs. 1-4. Where H(s) in Eq. 1, represents the first order GmC high pass filter transfer function and frequency shifting of this function to the left side by a ?y represents the first order complex notch filter shown in Eq. 4. The shifting of the frequency is proportional to Gm and inversely proportional to the capacitance C as shown in the Eq. 3.This technique can be used for high frequency image rejection applications. The following equations are derived from the implementation of a complex notch filter.
(1)
(2)
Where
(3)
(4)
As mentioned in the above Eq. 4, the complex notch filter is designed and it is shown in the Fig.1.
Brief description of Drawing
In the figures which are illustrated exemplary embodiments of the invention.
Figure 1 Proposed complex notch filter
Detailed description of the drawing
As described above the present invention relates to copyright fetching.
Figure 1 gives the view about the design of a notch filter using OTA. The filter shown in Fig. 1 is used to remove the noise in wireless receivers. The trance conductance Gm and capacitance C are used to control the filter for desired frequency response. The frequency response of the first order notch filter is best suits for Bluetooth wireless communication