**5.2. SILO oscillator concepts**

12 UKoLoS

Port

**Figure 10.** Synthesizer key components; left: VCO, right: half-circuit of single-pole double-throw switch

*LB* is realized as a spiral inductor without tuning capability. Tuning is available by varying *Cin*, which has to be tuned over a wide tuning range using variable MOS-capacitance circuits. For a minimum influence on the tuning range, *CP* has to be minimized. It consists mainly of the collector base capacitance *CCB* of transistor *T* and thus is given by size and bias conditions. *CS*, which is determined mainly by *CBE*, has to be maximized. Additionally, both varactor capacitance ranges have to be maximized. For a more detailed discussion, refer to [15]

The proposed pulsed ultra-wideband signal generation requires a switch after the frequency synthesizing PLL. The switch should have a minimum switching time in both on and off direction to enable the usage of very short pulses (in the 1 − 10 ns range). Additionally, a constant input port impedance is important in order not to change the loading of the oscillator. A switch circuit was designed based on [10]. The original work was aimed at a 22 − 29 GHz

UWB radar for automotive applications. Fig. 10, right, shows the half-circuit.

0.8 1 1.2 1.4 1.6 1.8 2

Time in s

**Figure 11.** Switch transient simulation: Output voltage signal (blue) in reaction to control voltage (red)

Output Voltage Control Voltage

1

VCB

Q7 Q8

Q2 Q5 Q6

x 10 −9 Port

2

Vc Vc

Q4

A B

Q9

VCS

Q1

Q3

VCC

RL RL

RE

C <sup>1</sup> C var

T

RCC C <sup>4</sup>

C <sup>3</sup>

L <sup>B</sup>

Cin

C var

−0.5

0

0.5

Voltage

change.

1

1.5

\*

V tune

I 0

C <sup>2</sup>

V Bias

Q Q

V CC

As the injection locking property is universally stemming from oscillator theory, any oscillator can in theory be employed for switched-injection locking. There is an interesting trade-off to be made when considering an oscillator configuration for SILO building: The oscillator *Q*-factor should be high and excess loop gain should be low for better phase noise performance on the one hand, but a high-*Q* oscillator with low excess loop gain takes longer to begin oscillation, which is critical for pulsed angle modulated signal generation. A careful balance between the two qualities has to be found.

Another consideration has to be put into the point in the oscillator loop where the signal is injected into. In a cross-coupled oscillator, the resonator and gain stages are directly connected to the output. This means that there has to be a buffering circuit for the injected signal which provides backward isolation, in order to ensure the oscillation frequency of the oscillator is not influenced by the circuitry connected to the tank.

For the design of the SILO circuits, we concentrated on resonator-based oscillators, as they typically show better phase noise performance than inverter-based ring oscillators. A demonstrator implementation in discrete components was used for initial experimentation and verification of the viability of our approach. This circuit was aimed at a frequency range of 6 to 8 GHz. Subsequently, a SILO IC based on a pulse generator and a cross-coupled *LC*-oscillator was designed and manufactured. In a final step, a harmonics generator was combined with a Colpitts oscillator to sample a 5.8 GHz-signal and emit a 63.8 GHz-signal.
