Emitter coupled oscillator

The emitter coupled oscillator (Fig. 17) is a circuit also providing one quartz crystal electrode grounded. For practical realization as a series resonance oscillator, a signal proportional to the current through the quartz crystal is amplified and fed back as a voltage. Since least gain is necessary for low impedance resonance, the resonance with the smallest impedance will preferably be excited. Phase condition is fulfilled for a frequency where the quartz crystal behavior is real, i.e., for/r. 

Current feedback amplifiers always consist of a diamond transistor (DT) and a buffer stage internally connected. The OPA660 [42] or its replacement OPA860 [43] allows separated access to both circuit parts so that a voltage-controlled current source (OTA) at a bandwidth of 90 MHz and a buffer stage at a bandwidth of 700 MHz are available. In contrast to normal transistors the diamond transistor, whose temperature-stabile operating point is internally determined, allows four-quadrant operation. The OTA provides the required almost-ideal transistor to design an emitter-coupled oscillator. 

FIGURE 15.2 Graphical interpretation of the structural model (a) electrical and mechanical analog of the microcollective or cluster (b) equivalent circuit for the emitter-coupled oscillator (c) the macrocollective a schematic cross-section of the droplet and its characteristics Vj, structural volumes or clusters 14, excluded surface volumes or interspaces 14, excluded bulk volumes or interspaces Si, internal separation external separation R, rigidity droplet boundary E, elasticity droplet boundary). 

The equivalent electrical circuit, rearranged under the influence of an apphed physical field, is considered as a parallel resonant circuit coupled to another circuit such as an antenna output circuit Thus, in Figure 15.4c, Wj, Cd, La, and Ra correspond to the circuit elements each Wd represents active emitter-coupled oscillator and Cd, Ld, and Rd, represent passive capacitive, inductive, and resistive elements respectively. The subscript d is related to the particular droplet diameter, that is, the droplet under consideration. Now, again the initial electromagnetic oscillation is represented by... 

FIGURE 15.4 Definition sketch for understanding the theory of electroviscoelasticity (a) rigid droplet (b) incident physical field, for example, electromagnetic (c) equivalent electrical circuit-antenna output circuit. Wd represents the emitter-coupled oscillator and Cd, and i d are capacitive, inductive, and resistive elements of the equivalent electrical circuit, respectively. Subscript d is related to the particular diameter of the droplet under consideration. (Courtesy of Marcel Dekker, Inc.) Spasic, A.M. Ref. 3., p. 854. 

The components connected between the emitter-follower and the currentsensing filter capacitor can be thought of as a resistor divider. An additional 0.17 V needs to appear at pin 7 (through a 1K resistor) so the amount of current that must be contributed to that node is 0.17 V/1K which is 170 pA. The capacitive coupling of the PNP to pin 7 essentially centers the oscillator waveform upon the current ramp. So,... 

---