Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicable.

Current Reuse Gains UWB LNA, Fig. 2

To achieve low power consumption, the width of transistor M1 is set to 260 μm, while the width of M2 is set to 200 μm. The inductances of Ld1 and Lg2 are 5.3 and 1.8 nH, respectively. Resistor Rb2 is used to provide bias voltage for transistor M2. The inductor Ld2 (2.3 nH) and resistor Rd (54 Ω) are chosen to provide inductive peaking for extending the frequency range and providing peak gain at the center of the passband, achieving nearly flat overall wideband LNA gain. The last stage of the LNA consists of transistor M3 and the current source is the 50-Ω buffer for measurement purposes. Capacitors Cin and Cout are DC blocks.

Current Reuse Gains UWB LNA, Fig. 3

The current-reuse amplifier functions as a two-stage cascade amplifier. The noise figure of the second stage contributed by both the MOSFET (device M2) and inductors Lg2 and Ld1 can be reduced by the gain of the first stage. With this design technique, not only is high gain possible, but low noise figure can be achieved simultaneously.

Current Reuse Gains UWB LNA, Fig. 4

Figures 2 through 6 offer simulation results for the proposed UWB LNA for simulations performed with the SpectreRF simulation program from Cadence Design Systems, utilizing a 0.18-μm silicon CMOS semiconductor process from Taiwan Semiconductor Manufacturing Co. (TSMC). Figure 2 shows the small-signal S-parameters, where it can be seen that the UWB LNA achieves average simulated gain of 10.6 dB from 3 to 7 GHz, with gain flatness of better than 1.5 dB. The maximum gain of 12.3 dB occurs at 5 GHz.

Current Reuse Gains UWB LNA, Fig. 5

Over the frequency range of interest, the input return loss (S11) is less than 7.7 dB, while the output return loss (S22) is less than 13 dB. The reverse isolation is less than -36 dB from 1 to 10 GHz, as shown in Fig. 3. The stability factor (K-factor) was also computed using S-parameter data and was found to be greater than 1 across the frequency range from 1 to 8 GHz (Fig. 4). This indicates that the proposed LNA is unconditionally stable across the frequency range of interest.

Current Reuse Gains UWB LNA, Fig. 6

Current Reuse Gains UWB LNA, Fig. 7

As Fig. 5 shows, the noise figure is better than 3.3 dB between 3 and 7 GHz with minimum noise figure of 2.6 dB at 4.3 GHz. The output power versus input power was measured for a single test tone at 5 GHz (Fig. 6), with a 1-dB compression point of about -10 dBm. The power consumption is only about 7 mW from a +1-VDC supply, which includes the power of the output buffer. 

Current Reuse Gains UWB LNA, table

The table summarizes the measured performance of the UWB LNA compared to previous works. The layout is shown in Fig. 7. The amplifier can achieve a wide bandwidth, high gain, and low noise figure while also operating with minimal power consumption—about 7 mW across a frequency range of 3 to 7 GHz.