Thomas Mattsson

A TX VCO for WCDMA/EDGE in 90 nm RF CMOS

A VCO is implemented in an RF 90 nm CMOS process and covers the frequency range 2.55-4.08 GHz. Drawing 19 mA from 1.2 V, the phase noise at 20 MHz frequency offset from a 3.7 GHz carrier is -156 dBc/Hz, meeting the phase noise requirement for GSM/EDGE and SAW-less WCDMA transmitter after frequency division by 2 or by 4. A second version of the VCO covers an additional 4.90-5.75 GHz range, at the expense of a higher phase noise in the added band. In this way, all currently operational WCDMA/EDGE bands can be synthesized by a single VCO working at the double or quadruple of the desired band.

A 9-band WCDMA/EDGE transceiver supporting HSPA evolution

The future of cellular radio ICs lies in the integration of an ever-increasing number of bands and channel bandwidths. Figure 21.2.1 shows the block diagram of our transceiver, together with the associated discrete front-end components. The transceiver supports 4 EDGE bands and 9 WCDMA bands (I-VI and VIII-X), while the radio can be configured to simultaneously support the 4 EDGE bands and up to 5 WCDMA bands: 3 high bands (HB) and 2 low bands (LB). The RX is a SAW-less homodyne composed of a main RX and a diversity RX. To reduce package complexity with so many bands, we chose to minimize the number of ports by using single-ended RF interfaces for both RX and TX. This saves several package pins, but requires careful attention to grounding. The main RX has 8 LNA ports and the diversity RX has 5, with some LNAs supporting multiple bands. On the TX side, 2 ports are used for all EDGE bands and 4 for the WCDMA bands.

21.6 A 2.4-to-5.3GHz dual-core CMOS VCO with concentric 8-shaped coils

Despite recent attempts to relax the phase-noise demands on voltage-controlled oscillators (VCOs) for cellular communications [1], mainstream radios require harmonic VCOs capable of a very low phase noise with moderate power consumption, associated to a large tuning range (TR) and a high insensitivity to interfering signals. Ideally, the TR should be in excess of one octave, since this allows the easy synthesis of all frequencies below those directly generated by the VCOs via repeated frequency divisions by 2. At the same time, the oscillation spectrum should be affected as little as possible by spurious (common-mode) magnetic fields impinging on the inductor coil in the VCO tank. This is a crucial requirement in modern radios, where there are more PLLs active at the same time, and particularly when (non-contiguous) carrier aggregation is implemented, since in this case the signal bands may be very close to each other. If an individual PLL is used for each band, the VCOs may oscillate very close to each other, or at frequencies that are harmonically related to each other, posing a very serious issue of mutual pulling through the respective magnetic field. And even if a single VCO is used [2], or two (or more) VCOs that are not harmonically related [3], it is nevertheless a good practice to design the tank inductor as insensitive as possible to external magnetic fields, which abound in and close to the radio IC.

A 2.8-to-5.8 GHz harmonic VCO in a 28 nm UTBB FD-SOI CMOS process

A 2.8-to-5.8GHz VCO designed in a 28nm UTBB FD-SOI CMOS process adopts a reconfigurable active core to save power at the lower oscillation frequencies, and to enable a trade-off between power consumption and phase noise at all frequencies. The UTBB FD-SOI CMOS process is instrumental to achieve a tuning range in excess of one octave at low power consumption, while the use of an 8-shaped tank coil yields a VCO that is highly insensitive to external magnetic fields. The VCO operates from 0.9V and has a figure-of-merit of 186-189 dBc/Hz, depending on the oscillation frequency and the configuration of the oscillator core. The active area of the VCO is 380 μm × 700 μm.

A transmitter CMOS VCO for WCDMA/EDGE

A VCO is implemented in an RF 90nm CMOS process and covers the frequency range 2.554.08GHz. Drawing 19mA from 1.2V, the phase noise at 20MHz frequency offset from a 3.7GHz carrier is −156dBc/Hz, meeting the phase noise requirement for GSM. A second version of the VCO covers an additional 4.90–5.75GHz range, at the expense of a higher phase noise in the added band. In this way, all WCDMA/EDGE bands can be synthesized by a single VCO.