A dual RF-receiver preceded by discrete-step attenuators is implemented in 65nm CMOS and operates from 0.3-1.0 GHz. The noise of the receivers is reduced by cross-correlating the two receiver outputs ...in the digital baseband, allowing attenuation of the RF input signal to increase linearity. With this technique a displayed average noise level below -169 dBm/Hz is obtained with +25 dBm IIP 3 , giving a spurious-free dynamic range of 89 dB in 1 MHz resolution bandwidth.
A spectrum analyzer requires a high linearity to handle strong signals, and at the same time a low NF to enable detection of much weaker signals. This is not only important for lab equipment, but ...also for the spectrum sensing part of cognitive radio, where low cost and integration is at a premium. Often there is a trade-off between linearity and noise: improving one degrades the other. Crosscorrelation can break this trade-off by reducing noise at the expense of measurement time. An existing RF frontend in CMOS-technology with IIP3 = +11 dBm and NF = 5.5 dB is duplicated and attenuators are put in front to increase linearity to IIP3 = +24 dBm. The attenuation degrades NF, but by using crosscorrelation of the outputs of the two frontends, the effective NF is reduced to around 5 dB. In total, this results in a spurious-free dynamic range of 88 dB in 1 MHz resolution bandwidth.
Wireless sensor networks have recently emerged in a wide range of applications. Many attributes are essential for such networks such as: low cost, small form-factor, limited peak power consumption ...and the ability to operate in harsh interference scenarios. Most of these networks do not require high data-rates to operate. In this respect, sub-sampling receivers have shown promising results but suffer from noise folding and interference aliasing. In this paper, a sub-sampling receiver in combination with cross-correlation is used to enhance sensitivity and interference robustness while maintaining the sub-sampling advantages. An architecture which uses two different sampling frequencies is proposed. It shows ∼2dB SNR improvement compared to traditional architectures due to cross-correlation and an additional ∼2dB for each doubling of integrations. For a BER of 10- 3 , the required SIR is reduced with 4.5dB, 11.5dB and 14.5dB after using cross-correlation with the same, half and quarter data-rate used respectively. These improvements allow for a lower-power and lower-cost implementation.
Highly linear CMOS radio receivers increasingly exploit linear RF V-I conversion and passive down-mixing, followed by an OpAmp based Transimpedance Amplifier at baseband. Due to the finite OpAmp gain ...in wideband receivers operating with large signals, virtual ground is imperfect, inducing distortion currents. We propose to apply a negative conductance to cancel this distortion. In an RF receiver, this increases In-Band IIP 3 from 9dBm to >20dBm, at the cost of 1.5dB extra NF and <;10% power penalty. In 1MHz bandwidth, a Spurious-Free Dynamic Range of 85dB is achieved at <;27mA up to 2GHz for 1.2V supply voltage.
A wideband IM3 cancellation technique for CMOS attenuators is presented. With proper transistor width ratios, the dominant distortion currents of transistor switches cancel each other. As a result, a ...high IIP3 robust to PVT variations can be achieved without using large transistors. Two prototypes in a 0.16 μm standard bulk CMOS process are presented: a Π-attenuator with four discrete settings obtains +26 dBm IIP3 and +3 dBm 1 dB-compression point (CP) for 50 MHz to 5 GHz with only 0.0054 mm 2 active area, and a similar T-attenuator system which obtains +27 dBm IIP3 and +13 dBm CP for 50 MHz to 5.6 GHz with only 0.0067 mm 2 active area.
Dynamic spectrum access relying on spectrum sensing requires reliable detection of signals in negative signal-to-noise ratio (SNR) conditions to prevent harmful interference to licensed users. Energy ...detection (ED) is a quite general solution, which does not require any knowledge of the signals to be detected. Unfortunately, it suffers from noise uncertainty in the receiver, which results in an SNR-wall below which signals cannot be reliably detected. Furthermore, distortion components originating from nonlinearity in the sensing receiver cannot be distinguished from true input signals, and is thus another effect that may obscure weak signals and cause false alarms or missed detections. Cross-correlation was recently proposed to reduce the SNR-wall and, at the same time, allow the receiver to be designed for high linearity. This allows for high-fidelity spectrum sensing, both in the presence of strong interference as well as for signals with a negative SNR. In this work, an integrated complementary metal-oxide-semiconductor prototype exploiting cross correlation is presented and tested in practice. The prototype achieves a high linearity of +25 dBm IIP3 at a sensitivity of -184 dBm/Hz, 10 dB below the kT noise floor. The measured results agree well with theory, and, compared to the traditional ED-approach, show both a significant improvement in sensing time, as well as a reduction of 12 dB in the SNR-wall itself. Overall, cross-correlation makes ED faster, more sensitive, more resilient to strong interferers, and more energy-efficient.
In the receiver path and in spectrum analyzers, typically gain control blocks are used to limit the incident power to the level that the receiver circuitry can handle without degrading the linearity; ...in the transmitter path stringent power control is also desirable. Although variable-gain amplifiers (VGAs) traditionally implement the gain-control block, attenuators based on FET transistors show superior performances on linearity, power handling capability and power consumption.
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