Wideband variable gain amplifier with noise cancellation

Abstract

A 1 -5 GHz noise-cancelling variable gain amplifier is presented in 0.18 mm CMOS technology that achieves a low noise figure (NF) below 4.8 dB over an 11 dB gain range. Its NF is as low as 3.2 dB for the gain range of 5.5 to 11 dB, while its input return loss is better than 13 dB over the entire gain range of 25 to 11 dB. The measured input-referred two-tone third-order intercept point (IIP3) at 2.4 GHz is better than 0 and 24.5 dBm at minimum and maximum gain, respectively. The circuit occupies an area of only 0.067 mm 2 and consumes less than 19 mW of power from a 1.8 V supply.Introduction: Variable gain amplifiers (VGAs) are very useful components in RF frontends because they serve as general-purpose gain blocks that can be used to precisely adjust the overall gain of a transceiver which may result from manufacturing tolerances in the other components in the system. A significant number of VGAs function on the principle of using a fixed gain amplifier followed by a variable attenuator to control the gain. That approach causes the VGA to have a high noise figure (NF) even in the high gain states, which makes them unattractive for use in receiver frontends. In this Letter, we demonstrate a new wideband VGA that addresses the NF problem over a wide gain range.Conventional wideband amplifiers such as the common-gate (CG) amplifier or the common-source (CS) shunt-feedback amplifier often have difficulties in achieving a low NF ( 3 dB) while maintaining a good impedance match, or suffer from limited gain and stability. Distributed and travelling wave amplifiers [1, 2] can provide a low NF, good impedance match, and flat gain over a wide range of frequencies, but typically consume a large chip area and power.More recently, inductive degeneration and multi-section inductorcapacitor (LC) networks have been reported [3] for wideband impedance matching and low NF. However, the use of several inductors on-chip consumes a large area and increases cost. Noise cancelling [4, 5] on the other hand is an effective approach for achieving a low NF and an impedance match simultaneously without the need for large inductors or feedback. Nevertheless, limited gain control has been reported if at all, and common variable gain techniques such as current steering, variable feedback and variable bias often suffer from deteriorated NF and input matching.In this Letter, a 1 -5 GHz noise-cancelling, gm-boosted amplifier is presented using 0.18 mm CMOS, with variable gain control introduced in its signal combination and noise cancellation circuit. Such an approach can provide a low NF (,4.8 dB) over an 11 dB gain range, and with a very good input match (,213 dB). The VGA is suitable for low-cost, low-power wireless communications, including 3 -5 GHz (low-band) ultra-wideband (UWB) digital radios, and 20-60 GHz millimetre-wave radios operating with an intermediate frequency (IF) in the 1 -5 GHz range.

A 0.4–3.3 GHz low-noise variable gain amplifier with 35 dB tuning range, 4.9 dB NF, and 40 dBm IIP2

“…Furthermore, the NF of the LNVGA is slightly higher than the NF presented by either [15] or [4], but with a much larger gain tuning range. The LNVGA gain tuning range is 17 dB larger than the results shown in [15] and is 19 dB larger than the results shown in [4].…”

“…The LNA uses g m -boosting [4] to make the selection of the M1 transconductance (g m1 ) flexible. The LNA input impedance needs to match the source impedance (R S ), that is 50 Ω .…”

“…Moreover, the huge gain control range is achieved due to the utilization of multiple stages, that takes its toll on linearity. The second methodology, on the other hand, can achieve a low noise figure, as shown in [4,15], yet these circuits are unable to get a large gain control range. The third methodology has been proposed in [9].…”

40-nm CMOS Wideband High-IF Receiver Using a Modified Charge-Sharing Bandpass Filter to Boost Q-Factor

“…Thus, the noise of M2 is partially canceled as explained further. The local feedback is created by connecting the drain of M2 to the gate of M1 [24], [25], which also boosts the g m of M1. The second auxiliary amplifier is created by using current-reuse [26], which saves power.…”

Codesign of Mixer-VGA Downconverter Blocks

“…It is well known that gain control blocks produce a significant amount of noise because their gain variation is usually accomplished through changes in resistance inside the circuit. Ideas on how to mitigate the impact of gain variations on the noise figure (NF) of VGA circuits are described in [9] and [10]. This paper reports on the design and experimental verification of two mixer-VGA downconverter blocks (DCBs) (Fig.…”