RMDA20420 データシートの表示（PDF） - Fairchild Semiconductor
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RMDA20420 Datasheet PDF : 12 Pages
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Application Information
The RMDA20420 can be used as an even harmonic multiplier or as an odd harmonic multiplier depending on the type of DC
biasing arrangement being used. Optimum DC bias is applied to peak the desired harmonic which falls into the 20 to 42GHz
passband. The following application information will detail the configuration and procedure for using the RMDA20420 as an
even harmonic multiplier and as an odd harmonic multiplier. Typical measured data is provided at selected frequencies
within the passband with the RMDA20420 configured as a doubler and as a tripler.
Multiplier Operation
The RMDA20420 is a four stage general purpose MMIC amplifier covering the 20-42GHz passband. The amplifier has a
steep gain roll off at the band edges and the input return loss of the amplifier is better than 10dB from 42GHz down to DC.
Any multiplier harmonics, which fall in the passband, will get amplified and any harmonics that fall below the passband will
get suppressed.
A deliberate design feature that makes the RMDA20420 an effective multiplier is the ability to independently bias the first
stage. This feature allows freedom to determine the optimum DC bias condition required to peak the desired harmonic and
suppressing the unwanted harmonics. Optimum DC bias conditions depend largely on factors such as fundamental
frequency, desired harmonic frequency, input power level, output power level and suppression requirements.
Test Set Up
The basic test set uses a source to provide the input signal at the desired frequency and power level. The DUT was biased
either as an even harmonic or odd harmonic operation and the output was observed on a spectrum analyzer. The power of
the harmonics was measured using the spectrum analyzer with all the cable losses accounted. Figure 5 shows the basic
test set used.
Source
RMDA20420
DUT
Spectrum Analyzer
Figure 5. Basic Test Set Up
Even Harmonic Operation
Even harmonics are generated whenever the symmetry of the input signal waveform is distorted. This is accomplished by
biasing the first stage operating point in a region of the I-V curve where the device is near pinch-off. In this condition, the
first stage becomes a half wave rectifier where conduction only occurs on positive half cycles of the input waveform. Thus,
presenting an asymmetrical waveform consisting mainly of positive half cycles which is rich in even harmonics to the
remaining stages of the amplifier.
For most even harmonic multiplier operations, the first stage is usually pinched off and the remaining stages are biased as
a linear amplifier. As an example, the RMDA20420 was evaluated as a doubler.
In the doubler operation, two drain voltages of +3.5V were used: One for first stage (Vd1) and the other (Vd2) for the
remaining 3 stages tied together as shown in Figure 6. Independent biasing of the first stage was achieved by using two
separate gate voltages. Vg1 was used for stage one and set to Vg1 = -1.0V (near pinch-off). Vg2 was used for the remaining
three stages. Vg2 was adjusted until Idq = 330mA.
©2004 Fairchild Semiconductor Corporation
RMDA20420 Rev. D
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