For high frequency bipolar design there are two parameters which are important in estimating the device performance. ( In actual fact the fmax of the bipolar device is equally important but is not detailed here). tF, the total forward transit time, is used for modeling the excess charge stored in the transistor when its emitter – base junction is forward biased and its collector to base voltage is VBC = 0.0. It is also needed to calculate the transistor’s emitter diffusion capacitance. Typically the tF varies with IC ( the collector current). Values of tF generally range from 0.3 nanosecond to a few or fractions of a picosecond for high frequency devices. fT is the transistors’s unity gain bandwidth. fT is defined as the frequency at which the common emitter, zero-load, small signal current gain extrapolates to unity. The roll-off is 6dB/octave. This information should be used to determine the performance required for particular device suitable for design at a particular frequency point. tF and fT are parameters used in models that drive CAD programs. In some programs the user can enter fT or tF directly while in others either fT or tF is converted from either parameter. fT can be measured using a small signal method. In this method the ratio Iout/Iin ( the current gain in a common emitter configuration)is measured for a range of frequencies from DC to the 3 dB point and beyond at a desired bias point. Then fT = product of current gain at DC and the 3dB frequency, i.e B0 X fb. Here B0 is the dc current gain and fb is the 3 dB frequency. Alternatively, another B and frequency value can be measured to determine fT. For example, at any frequency, fm, between 3fb and ft/3, the B value at that frequency Bm, is measured. Then fT = Bm X fm. It is recommended that multiple measurements be made to verify that fm lies in the 6 dB/octave roll-off region. Once fT is known tF can be obtained from it using the formulas described elsewhere in this blog.
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The input interface.
The frequency divider has a differential analog interface. The following parameters apply:
The minimum frequency that can be input is 500 Mhz and the maximum frequency is 6.0 Ghz.
The RF input level is 5 dBm to – 5 dBm. For lower frequencies make sure that the slew rate is
greater than 560 V/us. The input is biased by two 500 Ohm resistors connected to a 1.6V DC bias.
Therefore AC coupling is used at the input. These are two 100pF capacitors.
The output interface.
The output is single ended. The output driver is capable of sourcing and sinking 24 mA. The
equivalent output impedance is 50 Ohm. To avoid reflections it is recommended that the divider
work into a 50 Ohm load.
General operation.
The inputs are applied to the input SMA I/O. The product will work with both a differential input as
well as a single ended input. However, a differential input works best. The division ratio is applied
to the N1 and N2 control inputs as follows:
N2 N1 Division ratio
0 0 8
0 1 16
1 0 32
1 1 64
The logic levels are:
Logic level Voltage
1 1.4V minimum
0 0.6V maximum
The supply voltage interface.
The operating supply voltage is 3.3V typical. The quiescent (DC) operating supply current is 2 mA.
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RF Switch typical features
Supply voltage = Vcc = 0/+5 Vdc
Operatng temperature = TA = -50° C to 125 Deg C
Operating impedance = 50 Ohm
Input power for 1 dB
compression ( 5.0V system) = 37 dBm ( f = 0.5 to 3 Ghz)
Input third order Intercept = 64 dBm ( 0 to 5.0V system, f = 0.5 to 3 Ghz)
Operating frequency range = DC to 3 Ghz.
Insertion loss DC to 3 Ghz = 0.8 dB
Isolation DC to 3 Ghz = 14 dB minimum
Return loss DC to 3 Ghz = 20 dB
50% contl to 10/90 %
( ON/OFF) = 120 ns
Summary Specifications
Gain, Operating: 19.5 dB
Operating frequency range: 1.0 – 2700 Mhz
OIP3: (Pout = 19.0 dBm), -8.5 dBm
P1dB: 4.6 dBm
N.F: 4.2 dB
Supply voltage Operating: 3.3 – 5.5 Volts
Price: single unit $7.50, 100 units : $5:50.
Free delivery, shipping lead time 2 days.
30 day return policy, buyer ships.
Supply current Supply = 5.0V, 23.0 mA
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