Abstract: An attenuator circuit which has a small insertion loss and also has a broad tolerance toward the fluctuation of the element parameter. An attenuator stage having the largest attenuation quantity of a plurality of attenuator stages is formed with a .pi.-type attenuator stage, and an attenuator stage having the smallest attenuation quantity of the plurality of attenuator stages is formed with a T-type attenuator stage. In this way, an attenuator stage having a large attenuation quantity whose precision of the attenuation quantity is apt to be detracted is formed with a .pi.-type attenuator stage so that the precision becomes high, further, an attenuator stage having a small attenuation quantity is formed with a T-type attenuator stage so that the insertion loss can be lowered.

Abstract: A linear attenuator (23) for applications such as front/rear audio fading receives an input current to be programmably attenuated according to an input code at an input node (29). A transistor (30) is connected between the input node (29) and inputs of current-steering cells (40, 50, 60), which pass portions of the input current to either an output node (32) or a second node in response to the input code. An amplifier (22) has a negative input terminal connected to the input node (29), a positive input terminal receiving a reference voltage, and an output terminal connected to a control electrode of the transistor (30). The operational amplifier (22) and the transistor (30) together regulate the voltage at the input node (29) to prevent distortion of the input current by making the input node (29) a virtual ground node. Thus the attenuator (23) avoids nonlinearities normally associated with transistors and the need to duplicate a digital-to-analog converter (DAC) (21) providing the input current.

Abstract: An attenuator circuit having a resistive "T" network and a resistive "Pi network in parallel with said "T" network.

Abstract: A high accuracy programmable attenuator for accurately selecting and maintaining desired values of attenuation for a high frequency RF signal. The attenuator is comprised of a plurality of cells wherein each cell is comprised of an individual attenuator, a switch and a bias resistor. Each bias resistor is comprised of a plurality of individual resistors arranged in a binary sequence and wire bonds are used to short out undesired resistors for compensating for insertion loss and obtaining desired attenuation. The attenuators of the circuit are also arranged in a binary sequence so as to allow the user to select from a large variety of attenuations in small increments.

Abstract: A digital-to analogue converter for producing an RF output signal proportional to a digital input word of N bits from an RF reference input, N being an integer greater or equal to 2. The converter comprises a plurality of power splitters, power combiners and a plurality of mixers or RF switches connected in a predetermined configuration.

Abstract: A loss button for a traveling wave tube. The front and rear planar surfaces of the ceramic pill-shaped button body are of coated metallic composition. The periphery is uncoated to permit r.f. energy to enter the button through thee cavity of the planar, metallic spacer into which the button is inserted. By coating the body surfaces, the button itself acts as a resonant cavity for attenuation of a predetermined bandwidth so that the dimensional changes that occur during heating to the surrounding and adjacent metallic elements, including the cavity in the spacer for receiving the button and the adjacent braze washers, will not affect the attenuation band of the tube.

Abstract: A low current vector modulator for continuously varying the amplitude and polarity of an RF signal includes first and second hybrid couplers electrically connected at their input ports to an RF source. The characteristic impedance of the hybrid couplers is twice the impedance of the RF source. First and second PIN diodes are electrically coupled to 0.degree. and 90.degree. phase ports of the first hybrid coupler, respectively, and third and fourth PIN diodes are electrically coupled to 0.degree. and 90.degree. phase ports of the second hybrid coupler, respectively. The first and second PIN diodes and the third and fourth PIN diodes also are electrically connected respectively to first and second biasing sources. Varying the biasing provided by the first and second biasing sources varies the amplitude and phase of first and second output signals generated by the first and second hybrid couplers.

Abstract: An electromagnetically lossy liquid- or gas-tight fusion seal for use as a low pass radio frequency signal filter constructed as a matrix of glass binder and ferromagnetic and/or ferroelectric filler. Metal cased electrical filters are made by reflowing the material to form fused glass-to-metal seals and incorporating electrical thru-conductors therein which may be formed as inductive windings.

Abstract: An attenuator includes first resistors that are connected in series to each other at connection nodes and between an input node and a fixed voltage node, voltage output nodes coupled to the input node and the respective connection nodes of the first resistors, switches and corresponding second resistors being respectively connected in series between the connection nodes and voltage output nodes and commonly connected to an output node, and a load capacitance connected between an output node and the fixed voltage node. The phase between input and output signals is independent of the attenuation. A phase difference is added by the second resistor so that the phase shift determined by the voltage dividing ratio of the first resistors selected by closing a switch and by the value of the load capacitance is compensated.

Abstract: A fast settling, wide dynamic range vector modulator for use in an interference cancellation system or the like includes a quadrature hybrid which receives an RF signal and divides the signal into a primary in-phase component signal and a primary quadrature phase component signal. A first 180.degree. hybrid receives the primary in-phase component signal and provides first and second secondary in-phase component signals which are 180.degree. out of phase with each other. A second 180.degree. hybrid receives the primary quadrature phase component signal and provides first and second secondary quadrature phase component signals which are 180.degree. out of phase with each other. A first switching device selects one of the first and second secondary in-phase component signals, and a second switching device selects one of the first and second secondary quadrature phase component signals.

Abstract: A variable attenuator has a plurality of attenuation resistor units, a plurality of switching units, and a plurality of impedance compensation resistor units. The attenuation resistor units are connected in series for attenuating an input signal, and the switching units are provided for the attenuation resistor units. One of the switching units are selected in accordance with a digital control signal supplied from an external source. Each of the impedance compensation resistor units is connected in series with the respective switching units to compensate an output impedance to a specific value regardless of the state of the switching units. Therefore, the variable attenuator of the present invention can correctly control the level of an analog signal by a digital signal.

Abstract: A step attenuator using a PIN diode for use with microwave circuits. The step attenuator circuit provides for stepwise controlling the current applied to the microwave monolithic integrated circuit. The step attenuator circuit comprises a driver circuit and a attenuator circuit coupled thereto. The driver circuit that comprises a temperature sensor, a comparator circuit coupled to the temperature sensor for comparing the temperature value sensed by the temperature sensor to predetermined reference voltages and for providing a plurality of output signals that are indicative of a respective plurality of temperature values sensed by the temperature sensor, and a resistor network coupled to the comparator circuit that is adapted to set the respective values or current provided by the driver circuit.

Abstract: An RF step attenuator topology is optimized for use with GaAsFET switching devices, exploiting their high isolation while minimizing the effects of their relatively high insertion loss. The attenuator includes an attenuation network that has two inputs and two outputs, permitting four different attenuation levels to be selected by use of just one input switch and one output switch. The detailed embodiments feature high levels of attenuation (up to 140 dB in 10 dB steps), a minimum number of switches in the through-path (four), very wide band operation (250 KHz-2 GHz), and economical design.

Abstract: An attenuator circuit uses single point control to adjust the attenuation levels between first and second nodes. The attenuator is set-up as a .pi.-network with a pass transistor and first and second shunt transistors. Capacitors are coupled in the drain and source conduction paths of the first and second shunt transistors for DC isolation to float the shunt transistors. A control voltage applied at the drain of the pass transistor and the gates of the first and second shunt transistors controls the attenuation level. A parallel resistor and capacitor combination at the drain of the first shunt transistor provides tuning to match the input impedance of the attenuator to the sourcing circuit.

Abstract: A miniature potentiometer suitable for mechanical adjustment of microwave circuits is provided. Furthermore, there is provided a dual, ganged potentiometer also suitable for mechanical adjustment of microwave circuits. The dual, ganged potentiometer provides reliable tracking of tapers between the two variable resistance elements. Yet further, there is provided a complete, microwave, T-pad attenuator circuit which is mechanically adjustable. The T-pad attenuator uses two ganged potentiometers, whose tapers track in a known non-linear fashion. The tapers may be logarithmic.

Abstract: A voltage attenuation network includes one or more cascaded resistor ladder stages, with decremented voltage taps provided at successive cascaded steps within each stage. Each stage includes a termination step having a resistance value Ri equal to the stage input impedance, series step resistors with resistance values Ri(1-A)/A and shunt step resistors with resistance values Ri/(1-A), where A is a step-to-step voltage attenuation factor. The input resistances of each step within a given stage are substantially equal, eliminating the need for output buffers at the step taps. A pair of switches are provided for each step, including an output switch connected between the step input node and a common output line, and a shunt switch connected in series with the shunt resistor for that step. Only one output switch is closed at a time, and only the corresponding shunt switch for the same step is opened.

Abstract: An absorptive temperature variable microwave attenuator is produced utilizing at least two different thick film resistors. The temperature coefficients of the resistors are different and are selected so that the attenuator changes at a controlled rate with changes in temperature while the impedance of the attenuator remains substantially constant. Substantially any temperature coefficient of resistance can be created for each resistor by properly selecting and mixing different inks when forming the thick film resistors. Furthermore, attenuators can be created having either a negative temperature coefficient of attenuation or a positive temperature coefficient of attenuation.

Abstract: A variable electronically controlled phase shift circuit including a phase splitter stage including a 90 degree phase divider to split an RF input signal into 0 and 90 degree components. Each split signal is further split into two pairs that are displaced in phase by 180 degrees to provide, 0 degree, 180 degree and degree, 270 degree pairs. Four signals of the signal pairs are applied to a phase controller subcircuit wherein one of each of the two signal pairs may be attenuated by a control signal. The signal pairs from the phase controller sub-circuit are then summed and the summed pairs are combined into a single output signal. The phase of the output signal is controlled by varying the relative amplitudes of at least one of the component signals of the 0 degree, 180 degree and 90 degree, 270 degree pairs by means of the control signals on the phase control sub-circuit.

Abstract: An attenuator relay including encapsulation apparatus having an interior for enclosing an electro-mechanical relay and circuitry; an electro-mechanical relay having a number of contacts, the relay providing apparatus for closing a first circuit to allow current flow therethrough in a first condition, and apparatus for closing a second circuit to allow current flow therethrough in a second condition; and an attenuator circuit connected in the first circuit and enclosed within the encapsulating apparatus.

Abstract: Apparatus for measuring electromagnetic radiation from an electronic component in which a transverse electromagnetic cell has a coaxial connector for receiving radiation, a septum extending from the connector to a facing wall of the apparatus, the facing wall having a flat surface and formed from ferrite particles dispersed through rigid material. The rigid material is ceramic and conveniently the facing wall is made from ceramic tiles incorporating the ferrite particles. With this wall structure, the apparatus may be of small size suitable for measuring radiation or electronic chips or connector assemblies.

Abstract: An electronic attenuator device is provided whose attenuation characteristics are substantially insensitive to variations in component element parameters and ambient temperature changes. Advantageously, an attenuator device made according to the present invention may be constructed at substantially reduced cost without loss of attenuation precision.

Abstract: A limiting filter has nonlinear signal limiting devices integrally connected to the filter structure so that as the power level of input signals increase the nonlinear signal limiting devices decrease their impedance in response thereto, detuning the filter. Filter isolation thus becomes a function of both frequency and input power.

Abstract: A high frequency PIN diode attenuator uses an inductive element in parallel with the PIN diode. The inductor resonates with the parasitic capacitance of the PIN diode to increase the attenuation level.

Abstract: A main ladder attenuator has a series of resistors and switches for connecting corresponding resistors to an output. The controller has an auxiliary ladder attenuator connected to the main ladder attenuator in series and having a series of resistors and switches. Each of the resistors of the auxiliary ladder attenuator is provided for interpolating between the adjacent resistors of the main ladder attenuator.

Abstract: The present invention decribes a high-frequency attenuator using PIN diodes, which is especially intended as power control means in a radio-telephone transmitter, and in which the input and output impedances remain constant as the attenuation is varied. The attenuator comprises a longitudinal branch between the input and the output port, having PIN diodes (D1, D2) attenuating the RF signal, transverse branches connected with the input and the output port, each comprising a quarter-wavelength transformer (C1, Z1, C2; C4, Z2, C5) viewed from the signal path and a PIN diode (D3, D4). The same control direct current passes via all the diodes. In spite of the variations of the resistance of the PIN diodes, the input and output impedances of the attenuator do not change owing to the quarter-wavelength transformer.

Abstract: An attenuator assembly (38) employs circuitry formed on an attenuator substrate (44) having short voltage divider path lengths that allow the use of low-cost divider selecting relays (58, 60, and 62) while maintaining low VSWR and aberration levels through the attenuator. An interconnect circuit board (80) provides electrical power, control signals, a ground plane shield (108), and probe coding contacts (32) for connection to the attenuator substrate. The circuits on the attenuator substrate are laser-trimmed to obtain predetermined electrical characteristics prior to assembly in a completed attenuator assembly. The attenuator substrate rests on a recess (128) formed in top margin (127) of a cavity (120) formed within a housing (42).

Abstract: A high speed probe attenuator has an attenuator with a plurality of resistors connected in series between a probe input and an instrument output. A plurality of capacitors are coupled in parallel with pairs of the resistors in an interleaved fashion to spread the frequency correction along the attenuator. The output of the attenuator is coupled by a large diameter coaxial cable to a test instrument. The result is a high speed probe with no dribble-up effect and no overshoot.

Abstract: The balance of the volumes in right and left channels in a stereo play back system is controlled. The amount of attenuation of an attenuator provided in each channel is controlled. When the levels of right and left stereo signals are judged to be approximately the same, an oscillator is permitted to oscillate and the pulses from the oscillator are counted by a counter. In accordance with a voltage signal which corresponds to the level ratio of the right and left stereo signals, whether the counter must count upwards or downwards is determined. The balance is controlled in accordance with the amount of attenuation of each attenuator which is determined in accordance with the decoded count value. The completion of the control is detected when the level ratio of the right and left stereo signals alternately change after they become substantially equal, and the control is automatically finished.

Abstract: A double-.pi. network includes a pair of series resistors connected between input and output terminals. A plurality of FETs of different widths and/or in series with resistors, are each connected in parallel with one of the series resistors. Each FET is controlled jointly with an FET of the same gate size associated with the other series resistor, so that select ones of the FETs, or none may be conducting in parallel with the series in-line resistances. Another plurality of intermediate FETs having gates with different widths, are connected in parallel and separately controllable for coupling selectively the junction between the two in-line resistors to ground. Finally, an additional plurality of pairs of FETs couple the input and output terminals to ground. The FETs making up each pair have gates with the same width and are jointly controllable. The FETs in the different pairs have different widths and/or are in series with different sized resistors.

Abstract: A dual-gate field effect transistor attenuator wherein a variable active load (1) is applied to the second gate of the dual-gate field effect transistor (T1). The attenuator is particularly suitable for space telecommunications.

Abstract: A signal processing circuit is provided, such as a PIN diode attenuator for use in cable television signal distribution. The circuit includes a variable impedance device that is responsive to an input signal. The input signal is provided over a first range to vary the impedance in response to a control signal having an absolute value below a predetermined threshold. The input signal is provided over a second range in response to the control signal having an absolute value above the threshold. The first and second ranges are not contiguous. In a preferred embodiment, a zener diode is used to increase the drive current to a bridged-T PIN diode attenuator when the attenuator control signal reaches the zener breakdown voltage.

Abstract: A current controlled variable attenuator circuit using a current controlled resistor is disclosed. In paticular, the current controlled resistor and attenuator are particularly suited for use in hearing aids due to the resistor's and attenuator's easy implementation in bipolar integrated circuits. The current controlled resistor and attenuator also has wide application to other circuitry requiring controlled variable resistance elements having a broader linear response than previously available. The current controlled resistor consists of transistors having inherent non-linear characteristics which can be linearized by adding appropriate compensation circuitry.

Abstract: A first PIN diode is connected to the input side of a tuner at the front end of an FM receiver, in an AC coupled fashion parallel to the tuner. A correction inductance is connected parallel to the first PIN diode in an AC coupled fashion. The tuner is connected, at its output side, parallel to a series-connected circuit of a correction capacitor and a second PIN didode. The anodes of the first and second PIN diodes are supplied with an automatic gain control (AGC) voltage. When the AGC voltage varies, the resistances of the first and second PIN diodes vary in a manner to adjust the degree to which the correction inductance and the correction capacitor affect the resonance in the tuner.

Abstract: The precision programmable attenuator of the present invention makes use of a pair of non-interactive parallel connected divider circuits to provide a flat frequency response over a wide bandwidth. A first of these divider circuits is a low frequency divider circuit which provides a predetermined attenuation of low frequency signals. The second high frequency divider attenuates the high frequency signals and does not interact with the low frequency attenuator. Therefore, each of these dividers can be separately tuned independent of the other. The implementation of the low frequency divider is a resistive divider network which provides a DC coupling of the input signal to the output. The high frequency divider is comprised of an adjustable capacitor divider network which is automatically electronically tuned to obtain the desired high frequency gain response.

Abstract: Absorber elements for reducing electromagnetic leakage radiation, in particular in the vicinity of horn antennas, are in the form of ribs with a roof- or wedge-shaped cross section arranged such that the angle enclosed by lateral surfaces of the absorber elements is less than 90.degree., so that at least the leakage radiation impinging in general parallel to the center plane of the absorber elements arrives at a large angle of incidence, i.e. glancingly. In particular, if the angle of incidence approximately corresponds to the Brewster angle, the result is an almost complete absorption of the corresponding polarization components of the leakage radiation. The absorption effect can be further optimized by proper selection of the configuration of the roof- or wedge-shaped absorber elements.

Abstract: A signal level attenuating device having an analog attenuator and a digital attenuator which respectively include resistance attenuators. The resistance attenuators have the same attenuating characteristics and are mutually coupled. When one of the resistance attenuators is adjusted, the other of the resistance attenuators is simultaneously adjusted so that an analog signal and a digital signal respectively entered therein are attenuated at an identical attenuating factor. The digital attenuator further comprises an A/D convertor, a coefficient generator and a multiplier. The resistance attenuator in the digital attenuator attenuates a reference voltage and sends it to the A/D convertor. The coefficient generator computes an attenuation coefficient by which the digital signal entered therein is to be multiplied, based on an output of the A/D convertor. The digital signal is multiplied by the attenuation coefficient in the multiplier.

Abstract: An attenuation network comprises a T or a .pi. network and first and second regulating circuits for controlling it. The T or .pi. network has at least two variable resistances. A switch S1 permits selection of a desired attenuation value which is set through the operation of the second regulating circuit on the T or .pi. network, while the first regulating circuit acts on the T or .pi. network such that its input and output resistances are kept constant.

Abstract: A damping device for HF signals with an analog-energizable attenuator, for drift-free generation of the analog control signal, in which any damping characteristics and corrections that may be necessary can be taken into account in a simple manner and individually for each damping device using EPROM components.

Abstract: An electronically reconfigurable digital pad attenuator is disclosed using selectively controlled segmented field effect transistors in a passive, non-gain state as the principal impedance elements. The attenuator may be fabricated in the monolithic microwave integrated circuit (MMIC) format with a segmented gate field effect transistor being connected in each of the separate branches of a Pi pad, Tee pad, or Bridged Tee pad attenuator configuration. The individual FET segments are maintained in a high admittance "ON" state or a low admittance "OFF" state in accordance with the binary control potentials applied to the gate of each segment, the principal electrodes being maintained at a zero potential difference. The attenuation then becomes a function of the binary gate potentials applied to each segment and assumes one of a set of well-defined discrete values. The attenuator consumes minimum power, provides attenuation steps that are independent of GaAs MMIC fabrication process tolerances, i.e.

Abstract: Switches are cascaded for improved off-state attenuation. The first switch of the cascade comprises an L-type attenuator with series branch including a resistor and a shunt branch including a Zener diode. A bias network coupled to the attenuator and to the second switch of the cascade connection controls the diode bias for operation at a specific forward conduction when the second switch is open and for operation at a specific reverse bias condition when the second switch is closed for causing the attenuator to provide the plural functions of (1) enhancing the switch off-state attenuation, (2) providing over-voltage and overcurrent protection for input transients of either polarity and (3) providing a predetermined output DC level when the second switch is on for establishing the DC bias of a subsequent circuit, such as an amplifier, the DC bias so supplied being in a tracking relationship with DC power supplied to the subsequent circuit.

Abstract: A high performance attenuator configuration divides a signal path into a plurality of parallel attenuator paths, each path having a predetermined attenuation value. A switch for each attenuator path is provided to couple selectively one of the attenuator paths to an input connector. Each attenuator path has an FET buffer amplifier, and the outputs of the FET buffer amplifiers are input to an electronic switch or multiplexer. The electronic switch selects the FET buffer amplifier output to be passed on to an output drive circuit.

Abstract: An ajustable switched capacitor circuit comprises a first stage, a second stage and a switched capacitor circuit coupling the output of the first stage to the input of the second stage. The operating parameters of the second stage are a function of the effective resistance of the switched capacitor coupling circuit. An attenuator interposed between the output of the first stage and the input of the switched capacitor coupling circuit controls the charging voltage of the switched capacitor coupler thereby controlling its effective resistance and parameters of the output stage. The signal loss through the attenuator is continuously adjustable responsive to an external control voltage to obtain continuous control of various output stage parameters. The output stage may comprise a filter having the parameters of its transfer function determined by the effective resistance of the switched capacitor coupling circuit.

Abstract: A binarily weighted FET attenuator implemented in integrated form. The resistance of the vertical branches to the horizontal branches is at a ratio of 2:1. Each vertical branch includes a FET switch for switching between ground and a summing amplifier and each horizontal branch includes a FET permanently biased to conduct. Thus, variations in the value of r.sub.on, the resistance of each FET when conducting, due to fabrication process and temperature are compensated for due to the presence of FETs in both the vertical and horizontal legs of the attenuator.

Abstract: A capacitor is charged and discharged through switch selectable resistors from regulated DC voltage supplies and clamping diodes to provide the bias signal to control the rise and fall times of the RF output pulse of a PIN diode attenuator. An isolation buffer isolates charging and discharging transients from the bias signal. An adjustable AC gain and adjustable DC offset inverting amplifier provides the isolation buffered signal to a high impedance, very low output AC impedance source for driving the bias input of the PIN diode attenuator. The DC offset is provided by an adjustable regulated voltage source coupled to the inverting amplifier.

Abstract: A variable field effect attenuator suitable for providing digitally controlled attenuation characteristic is disclosed. The attenuator can include a first semiconductor region connected in a series path between the input and output terminals and at least one shunt semiconductor region connected between the series path and a reference potential conductor. First gate electrodes are arranged to operate with the series semiconductor region and second gate electrodes are arranged to operate with the shunt semiconductor region. Gate electrode control lines are connected to selected gate electrodes so that digital signals can be selectively applied to the gate electrodes to render the semiconductor material associated therewith either conductive or nonconductive to provide a plurality of predetermined amounts of attenuation between the input and output terminals in response to a digital code.

Abstract: In a monolithically integratable microwave attenuation element, the attenuation is switchable between various, discrete values and the signal experiences only a small phase shift when switched between the individual attenuation values. The drain-source paths of field effect transistors (Q1, Q2, Q3) in the attenuation element are arranged in a PI configuration. Resistors (R11, R22, R33) are connected parallel to the drain-source paths of the field effect transistors (Q1, Q2, Q3) that are arranged in PI configuration.

Abstract: A modified progressive impedance ladder network has a plurality of cascaded resistive sections. Each of these sectiions has at least one resistive element and a single switch with values selected such that the section input impedance is larger than the output impedance of the preceding section.

Abstract: An attenuator element has a reference path and a relative attenuation path. The reference path is formed by a T-network of two FETs operated in the passive mode and a shunt path and the attenuation path is formed with a similar structure, with the FETs in the shunt path having a different channel width. Instead of a T-network, a Pi-network of transistors can be used. The respective gates of the FETs along the reference path are connected to a first control input corresponding to either zero volts or the pinch-off voltage and the respective gates of the transistors on the attenuation path are connected to a complementary control input having a voltage corresponding to the other of zero volts and the pinch-off voltage. Another type of attenuator element is formed with a reference path having a transmission line and an attenuation path formed by a resistive T-network, with the attenuation and reference paths being alternately selectable by two single pole, double throw switches.

Abstract: A monolithic microwave integrated circuit (MMIC) phase shifter is implemented in push-pull configuration with the quadrant selection and vector modulation functions combined. These functions are provided by four sets of adjustable gate-width dual-gate FETs and a pair of lumped element filter networks with a relative differential phase shift of 90.degree..

Abstract: A variable FET attenuator uses feedback in a control loop to correct the attenuator automatically for input/output return loss as the attenuator is varied with a control signal input. Both the series and shunt variable FETs are set to the proper conductance to maintain a proper input match with a desired attenuation value. A second, reference attenuator circuit provides feedback control of the primary attenuator circuit through an operational amplifier. The reference circuit is designed to be electrically equivalent to the attenuator circuit in terms of characteristic impedance. The control nodes, and attenuation control signal input and an output from the operational amplifier, are paralleled so that both the reference and primary attenuator circuits behave identically, without having to RF decouple the feedback loop from the attenuator circuit. Preferably, identical bridged-T variable attenuators are used for both the attenuator circuit and the reference circuit.