Ok, now that I've got some parts on order, I wanted to take some time here to help others that may still be reviewing this thread - on what all the EKL parts appear as.
To review:
Wanted to show this too...
Also...
In order to understand the one, the other must also be understood.
... The Needs of the Many ...
... Outweigh the Needs of the Few ...
... Or the One...
The Bipolar can generate it's own bias, without the need for an external voltage presence at the Base, as long as it's Base has a means to Drain off power it receives, and GENERATES, so they use a Bias Resistor network to help the Transistor turn on, but not as a switch, but as a LINEAR device by allowing the power flowing into the Base, a means to escape from it as it too - is a Reactive element when you apply an RF power to the "P" Junction of the NPN like the 2078.
As long as you have power that flows into it, and give it a way to flow out of it (Base) the Transistor can work much like a Linear device.
MOSFET's are a little too sensitive to these matters, and require a level of care on their Inputs since the Gate itself is insulated, Isolated from the power flowing in the Substrate underneath it.
They need a voltage presence to generate the Field that makes the "Field effect" part of the MOSFET work, or turn on.. Current can't flow into it, so you need to supplant this power to allow the voltage to appear on the Gate, but let the Current flow thru the Bias in such a fashion that the Gate simply follows the Input thru the Voltage level Change - this can allow the MOSFET to loosely work as a Linear device - you adjust the Voltage by allowing Power to flow thru a DIVIDER circuit that can leave the Gate to see only the Voltage changes - the Current portion of the work, can then flow thru the Divider. You can also apply a Resistor to the Gate lead as needed to reduce the effects the Impedance changes when Current rises faster than the Divider can remove it in certain conditions..
So now, taking the above, we mentioned the BASE of a BJT can generate its' own power thru the PN junction the Collector and Emitter present the Base - all being interconnected directly. IF you let this power flow thru the Bias network properly - the Bipolar can attain a Class of Operation by itself and the Bias - only the power being applied has to have a means to stay limited in levels (controlled Dynamic Range) - so you develop a Bias Network and use Resistance to offset the complex Reactive elements the DC Rectified and AC/RF present. Understand that current and voltage appear during the operational condition in both DC and AC/RF signal.
What we want, is to preserve the shape and condition of the input signal.
Capacitance is often used as a means to provide an RF a way out of the circuit when Power levels and the Bias itself can exceed a given level - it's not as simple as this, but another term to help us in understanding this is ADMITTANCE.
Admittance
In electrical engineering, admittance is a measure of how easily a circuit or device will allow a current to flow. It is defined as the reciprocal of impedance, analogous to how conductance & resistance are defined. The SI unit of admittance is the siemens (symbol S); the older, synonymous unit is mho, and its symbol is ℧ (an upside-down uppercase omega Ω)
The MOSFET only requires the Voltage of those signals to appear on the Gate - and on top of that, you also need a means to allow for the Gate to track the signal not as a power curve, but as a voltage parameter.
The Bias network can be thought of as a work room - The Resistor and Diode - form 1/2 of a Directional Power Divider circuit, the other Resistor then provides the power curve and offsetting Resistive element to balance out the power delivery into the Gate. This tracking needs to be done without saturation or skewing the Voltage - you want the Gate to Follow, or Track the Signals' Voltage condition.
If not carefully considered, current can skew these results and the Gates own Reactive elements of capacitance it presents, can alter the way the signal can enter and produce work.
The Diode and Two Resistors.
They only produce work within themselves
- Note: They loop; from and back into, Ground.
They only function as a means to obtain Directional control and voltage from the input signal.
It's where you tap from, that determines not only the level of voltage to set your Gate's ON Threshold by,
but also the amount of power that remains in the circuit to provide the Voltage follow condition the Gate needs to track to stay linear.
- Too much current into the Gate doesn't damage it as much as it will damage the MOSFETS ability to properly follow the voltage results this circuit is supposed to track.
- In Regards to the Diodes Directional Power flow, Remember too, that the Devices like IRF520 and 13N10 as well as any other type of MOSFET construction, you should follow it's Enhancement type - in these cases of discussion, we are presuming "N-Channel" devices.
So you make the Divider with two parts, one main part, is where you want to set the operation of the Gate to follow. In other words, where do you want to go today can be thought of as the approach. How hard the work is, is the Voltage - so your Resistance then must be thought of as the Effort that must be used to provide it. The Diode simply is a Direction in which to provide the work to flow in.
IF you only had a "cap" - you'd have AC passing into the Gate - and due to the Capacitance the Gate has - it too is a form of work and works AGAINST your signal - two caps in series will exhibit capacitance of less than that of the smallest value component - so now you have TWICE the work effort it takes to even send in work to be done.
That is where the Resistors can take some of the effort the Capacitance has against your work. It can also give your power levels some range of effort to work in, so they too, don't over do it and possibly destroy the Gate.
But you still need Capacitance - large enough, to overcome the "lackadaisical" effects the Gate's own capacitance presses back as. You need to put in extra power to overcome the inertial effects the Gate Capacitance has in this.
So, you set up your system to provide a direction of power, and the Resistors then provide the tap points in which the Gate runs (Operates) or "sees" the turn on voltage for, the other Resistor then simply allows power to be removed from this input Gate condition allowing the Voltage to rise and fall tracking the Signal as it comes into this circuit. The Resistors simply use the Signal as a means to apply an Effort to the power DIRECTION and the Signals' own power level - when Rectified into a DC Voltage becomes the Turn On Threshold parameter.
We then uses the Resistors as a means of Work-effort and to allow power to escape from the circuit. Voltage simply follows the effort - like a pair of eyes that are watching-copying every move, only as a view from the Voltage standpoint.
In the first Graphic, I show that the user placed the Diodes on the back foil pad, and note where the Resistor is.
Since Diodes themselves are semiconductors - they have an inherited Intrinsic trait of appearing as a heavy capacitance "spike" when they are reverse biased. A trait due to their Doping - that can lessen the ability of the Resistors to overcome the capacitive effects the Gate and Input Capacitance has - as well as a Switching issue of noise and a transient spike that will occur during the Didoes Cutoff during an RF cycle or excessive AC input from Audio.
So again, they (look above for Reference) put the Diode at the END of the circuit to provide some distance of it's Intrinsic Reactive Elements. The Ohmic value of the Resistor can offset it by as an effective Resistive controlled effort against Reactive elements and their vectors of power, impeding the directional and input signal power flowing thru the circuit (Buffer).
- It is easier to think of Gate capacitance as a level of work it will take to make the Gate reflect the input signal.
- The Higher, or larger value the Gate Capacitance is, the hard it will be to make it work.
- This means lower (less ohmic) resistor values are needed to lessen the Charge that remains on the Gate itself when the Signal changes in level or direction. It charge has to be removed to allow the Device to track input signal level as a Voltage component.
- Higher input capacitance can help provide more signal in which to apply the circuit above and obtain the level of control and drive. But the drawbacks are the drive level and the ability of the circuit to skew or degrade the signal.
- The Diode is required in the circuit to attain a form or direction for power to flow in the circuit and as to WHERE your TAP POINT is, you use the MOSFET's Channel P or N as your Direction.
- Once Direction is established, and the Gates' Capacitance latent charge can be overcome - then the rest is simply to develop the voltage divider and set your Gates On Threshold.
- In the Realm of Class Of Operation, this type of circuit being used is more for Class C or Class D type.
- This design is not effective for SSB use, for low-level signal may be too weak to even attain the Gate's Turn On Threshold voltage to amplify, so then another FEEDER bias approach is needed (like TX Voltage as a means to provide power to supplant this circuit)
- This design is most effective for FM, AM, PWM and CW use
Even the Banded end, being the Cathode, allows the Above Ground Signal presence (more positive with respect to ground) a means to approach or Admittance allowed - into the Gate and the Field Effect. You do not want to alter the Admittance - at least not without consideration as to how large of the Gates' "plate" will affect the signal as it propagates into the MOSFET.
So you place the more reactive elements of the Bias further away from the Gate - in this example, by placing a resistor in front of the Conjugate-mess the Intrinsic impedance the Diode will appear as.
The Rectification can still occur.
However, the Resistor position within the circuit can help reduce the Diodes reactive effects - yet must have a low ohmic value that allows current to flow into and out of the Bias system and provide the Rise in Voltage necessary to make the Gate work the device linearly..
Voltage will follow the current according to the levels of Resistance (IF properly chosen in Values to offset Reactive properties of Capacitance and Diodes own Rectification) and rise of DC values and is how the Divider; acting as a unit will then let the power flow thru, in both ahead of and behind the Diode in Directional flow or pressure provided by the Rectification that occurs that is the Voltage that it develops.
- It shows as a difference in charge between the Diodes Junction layers;
- it's this Charge separation and Voltage rise effect and process we desire,
- not it's power by the Current the Device can generate.
- The purpose of the Resistors are to control the AMOUNT of flow as well as the Level of flow; in a given Direction, as well as to allow the current that develops in the circuit a means to leave the circuit without altering the input signal.
- -. a secondary condition of the Resistors also takes the Diodes Intrinsic switching effects from injecting, affecting the Signal we want to amplify.
- Capacitance in both the Gate and in the Input level of the Circuit itself - will generate a co-circulating DC current within this circuit, so care must be taken to allow this current - power flow, a means to remain controlled (Empty out of) and remain at a level that does not degrade the Input Signal.
- That Effort; it's in getting the rise (Admittance and Voltage) and fall (exit of Current) balance by using that Resistor divider. The Values chosen and their placement within the circuit, provides for it, as this mechanism to balance out the Reactive.
- We then can place the action of direction, or put the RF signal, (a means to "Float") into a more true Balanced condition in the Ground plane "Field effect" of the Gate, as the Field effect occurs over a highly positive charge flowing underneath.
So the AC / RF to DC Balance condition can also be attained by using the Negative Cathode side, the Signal being Positive with respect to Ground condition can also provide the best transfer of Signal by using Negative Voltage field presence to provide the Offset condition; being that these MOSFET's being used here are an N-Channel Device.
EDITS:
are for the Verbiage - Ugh!
