EL6201CW-T7_04 데이터 시트보기 (PDF) - Intersil

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EL6201CW-T7_04

Low Power 430MHz HFM Oscillator w/Disable

Intersil 

EL6201

waveform is a squarewave, and inductive loads can cause as

much as 1V of overshoot. This does not mean that the

current delivered to the diode has overshoot - just the

voltage seen at the EL6201 output. Measurements show that

the EL6201 output edge rate is about 300psec - a speed

nearly impossible to deliver over practical interconnects to

the diode.

The L Series of Figure 22 must be carefully chosen. The

goal is to get a series reactance of around 70Ω at 300MHz,

so 40nH would suffice. The inductor should be shielded to

reduce EMI and have no saturation effects at the supply

currents drawn by the EL6201. Finally, there should be no

self-resonance at the operating frequency or its harmonics.

Also important is circuit-board layout. At the EL6201’s

operating frequencies, even the ground plane is not low-

impedance, and ground loops should be avoided. Figure 23

shows the output current loops:

RFREQ

RAMP

SUPPLY

BYPASS

SOURCING CURRENT LOOP

GND

(8-PIN

PACKAGE)

SINKING CURRENT LOOP

LOAD

FIGURE 21. OUTPUT CURRENT WAVEFORM - 1GHz

BANDWIDTH

General Considerations

EMI and Grounding

From an EMI point of view, the edge rate of the output

current is much more important than that of the output

voltage. The components are generally small and will be

placed over a ground plane, so antenna effects that launch

voltage-mode EMI are small. Measurement shows that a

practical current edge rate is about 1nsec., so interconnect

should be over a ground plane and short to minimize

inductively launched EMI. Most EMI seems to come from the

supply wires connected to the diode/EL6201 board. The

internal resistance and inductance of capacitors prevents

perfect bypass action, and 150mVP-P noise on the lines is

common. There needs to be a lossy series inductance and

secondary bypass on the supply side to control signals from

propagating down the wires. Alternatively, a series supply

resistor can be used, which will also be useful in reducing

EL6201 power dissipation. Figure 22 shows the typical

connection.

VS

EL6201

GND

L Series: 70Ω reactance at

300MHz (see text)

+5V

0.1µF

Chip

0.1µF

Chip

FIGURE 23. OUTPUT CURRENT LOOPS

For the sourcing current loop, the current flows through the

supply bypass capacitor. The ground end of the bypass thus

should be connected directly to the EL6201 ground pin

(output ground pin of the 8-pin package). A long ground

return path will cause the bypass capacitor currents to

generate voltage drops in the ground plane of the circuit

board, and other components (such as RAMP and RFREQ)

will pick this up as an interfering signal. Similarly, the ground

return of the load should be considered as noisy and other

grounded components should not connect to this path.

Slotting the ground plane around the load’s return will

eliminate adjacent grounded components from seeing the

noise.

RFREQ and RAMP Interfaces

RAMP and RFREQ should be connected to the non-load side

of the power ground to avoid noise pick-up.

Figure 24 shows an equivalent circuit of these pins. VREF is

roughly 0.35V for RFREQ and more accurately 1.17V for

RAMP. The RAMP and RFREQ resistor should return to the

EL6201’s ground very directly lest they pick up high-

frequency noise interference. They also should have minimal

capacitance to ground. Trimmer resistors can be used to

FIGURE 22. RECOMMENDED SUPPLY BYPASSING

7

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