An on-chip wideband and low-loss duplexer for 3G/4G CMOS radios

Abstract

A wideband integrated RF duplexer supports 3G/4G bands I, II, III, IV, and IX, and achieves a TX-to-RX isolation of more than 55dB in the transmit-band, and greater than 45dB in the corresponding receive-band across 200MHz of bandwidth. A 65nm CMOS duplexer/LNA achieves a transmit insertion loss of 2.5dB, and a cascaded receiver noise figure of 5dB with more than 27dB of gain, exceeding the commercial external duplexers performance at considerably lower cost and area.

Optimum Single Antenna Full Duplex Using Hybrid Junctions

“…A number of transformer configurations can be used, including auto-transformers [36], [37], 90 or 180 hybrid couplers [1], [34], and hybrid transformers [31]. Fig.…”

“…EB duplexers must not only provide high DM isolation in order to reduce self-interference, but must also protect the receiver from CM signals, which can cause Low Noise Amplifier (LNA) device breakdown due to the large voltage swing at the LNA input. In [36], a prototype auto-transformer based duplexer has been shown to provide a 60dB isolation bandwidth (the bandwidth over which at least 60dB of isolation is achieved) of over 50MHz for DM signals, however this architecture provides no CM isolation, making it unsuitable for all but low transmit power applications. Hybrid transformer based implementations, however, can provide CM isolation, making them preferable for most modern wireless applications.…”

A tunable differential duplexer in 90nm CMOS

“…In Fig. 1(a) the single-ended version from [2] is shown; when the balance impedance equals the antenna impedance, the PA signal appears as an equal swing on the antenna and balance sides, and ideally no signal couples to the LNA side. However the unavoidable capacitive coupling between the primary and secondary windings of the transformer will cause a portion of the PA signal to couple as a common-mode signal to the LNA side [3].…”

“…In the extreme case where an autotransformer, i.e. a center tapped inductor, is used as a hybrid for lower loss [2], the entire PA signal appears at the LNA inputs potentially causing oxide breakdown of the LNA devices. It should be mentioned that an AC grounded center tap in the secondary windings of a hybrid transformer can reduce the common-mode signal coupled to the LNA, by reducing the common-mode impedance seen on that side.…”

“…In [1], [2] an integrated duplexer based on electrical balance, rather than frequency selective filtering, was introduced, with the topology in [2] offering wider isolation bandwidth. A drawback of that technique is that the PA signal couples as a common-mode signal to the differential LNA inputs.…”