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An innovative solution to design phase and quadrature pulsed coupled oscillators systems through electromagnetic waveguides is described in this paper. Each oscillator is constituted by an LC differential resonator refilled through a couple of current pulse generator circuits. The phase and quadrature coupling between the two differential oscillators is achieved using delayed replicas of generated fundamentals from a resonator as driving signal of pulse generator injecting in the other resonator. The delayed replicas are obtained by microstrip-based delay-lines. A 2.4 - 2.5 GHz VCO has been implemented in a 150 nm RF CMOS process. Simulations showed at 1 MHz offset a phase noise of -139.9 dBc/Hz and a FOM of -189.1 dB.

Pushed from the ever-increasing demand in the electronic devices market for personal mobile devices and for wireless sensor networks, the research on innovative techniques for lowering energy requirements and costs of the electronic hardware is an extensively treated subject. At the core of every of above mentioned device, certainly an RF-IC resides, since it accomplish the necessary functional block for the establishment of a RF communication. In particular, the upconversion/downconversion task in RF-ICs usually represents the subsystems involving the major wafer area and power consumption. Toward the reduction of both areas occupation and power are placed CMOS Pulsed Bias Oscillators (PBOs). The PBO approach represents a technique exploiting the time-varying properties of electronic oscillators system. This technique can be applied to oscillators constituted of harmonic resonators refilled by active devices acting as current generators. This oscillator class aims to reach high performance in terms of phase noise with reduced energy requirements with respect to their non-pulsed counterparts. Basing on the results of Floquet Theory applied to a single oscillator [

The outputs of a phase and quadrature oscillator are phase shifted replicas of a fundamental frequency

The voltage maximum of a delayed sinusoid from a resonator can be hence used to generate refilling pulses, synchronized at output voltage minimum of another resonator. Thus in this paper, we propose to couple two oscillators applying a fixed delay of

In a lossless transmission-line the secondary constants

ligible and the transfer function between the input port, at

where

If

where

tablished considering the condition

in a phase and quadrature PBO (PQPBO) are needed.

The reference schematic of the oscillator is presented in

The losses are compensated by the introduction of the current pulse generators (PG) as showed in

Typical output signals of a phase and quadrature oscillator

Oscillator schematic of the proposed PQPBO

Pulse generator schematic

The following description refers to the PG recharging the

This bound grants an effective isolation of the resonator from the loading effect of PG input. Then, a triple- well is used to connect the

transistor width and length, respectively. If

glecting the dependence on transistor operating region), we can derive an upper bound for

scending from Equation (3) it implies

This bound must be accounted because an eventual low

To this aim, the DL is introduced to obtain the delay necessary to synchronize the refilling instant. The values of

The Polarization-Unit (PU), formed by

the driver transistor gate

and, descending from this choice, the derivation of the equivalent resistance,

where

ter-wave DL transformer loaded by the source follower. In

rapid exponential decay than

We notice in

Finally, the

It worth noticing the

Follows the DL matching description. In first approximation, DL is described with its secondary constants

imposed because of the resistive matching, but the value of

In

The delay-line is characterized by the transfer function on the

that takes into account

condition

The DL unit is implemented through a waveguide structure such a microstrip. As a first microstrip design step, literature formulas [

In

Reflection coefficient as a function of

Detail of layout of the proposed folded microstrip delay-line

The distance

If the condition in Equation (10) is not respected, the scattering parameters variation also depends on the

The microstrip reported in

Simplified folded microstrip delay-line

The value of

The length of the microstrip is initially chosen by Equation (9). Progressive adjustments of the

The oscillator has been implemented in the LFoundry

In architecture proposed in [

In the first comparison the oscillation amplitudes are kept at a fixed level of

In

In

lation is not directly related to the overall quadrature phase error between the tank node voltages signals, since the receiving resonant tank undergoes to a pulling due to the whole current pulse rather than to the position of the peak only. This phenomenon results in an attenuation of the quadrature error of about an order of magnitude in phase degree, allowing the phase error between voltage signals to be lower than

The phase noise results are presented in

As expected from a pulsed bias architecture the phase noise improvement is consistent especially at low offsets. However, to avoid bias dependence on results, we set the comparison at

According to

In the second comparison we gather a list of recently proposed phase and quadrature VCO architectures with both coupling based on active devices and on passive components. The results are reported in

In this paper a PQPBO based on a novel coupling method has been proposed. The coupling method adopts a delay-line implementation with an extremely compact meander microstrip structure. The design equations for the PQPBO, with a dedicated section on the DL optimization, have been pursued. The PQPBO has been implemented

PSS transient result of and nodes voltage

PSS transient result of voltage (continuous line) driving the PG injecting current (dotted line) in tank node

Phase noise results for the PQPBO (black trace) and for the refe- rence oscillator (red trace)

. Comparison with literature phase and quadrature VCOs

Reference | [9] | [10] | [11] | [12] | [13] | This Work |
---|---|---|---|---|---|---|

−115 @1MHz | −129.5 @1MHz | −125 @1MHz | −111 @1MHz | −134.8 @1MHz | −139.9 @1MHz | |

Freq. Range [GHz] | 5.0 - 5.7 | 2.4 - 2.6 | 4.9 - 5.5 | 6.9 - 7.3 | 1.8 - 2.2 | 2.4 - 2.5 |

Process [nm] | 180 | 180 | 250 | 180 | 180 | 150 |

FOM [dB] | −177.0 | −189.0 | −185.9 | −184.6 | −185.4 | −189.1 |

Quadrature Error [deg˚] | 0.36 | <1 | 2.6 | 2 | ≥0.7 | <0.1 |

Measured/ Simulated | M | S | M | M | S | S |

at LVS level in a LFoundry