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EL4083CN Datasheet(PDF) 8 Page - Intersil Corporation |
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EL4083CN Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 14 page 8 EL4083 IX and IY (Multiplier) Inputs and Offset Trimming The IX and IY pins are low impedance (IZ dependent) virtual ground current inputs that accept bipolar signals. The input referred clip value is equal to IZ × 2 while the full scale value has been chosen to be 1.25 × IZ to maintain excellent distortion and linearity performance. Operating at higher full scale values will degrade these two parameters and, to some extent, bandwidth while improving the signal to noise performance, feedthrough and control range. The EL4083 is fundamentally different from conventional voltage mode multipliers in that the available input range can be tailored to accommodate voltage sources of almost any size by selecting appropriate input series resistor values. If desired, one can interface with voltages that are much greater than the supplies from which the part is powered. Current source signals can be connected directly to the multiplier inputs. The parts’ dynamic range can also be tailored to a large extent for a current signal by the appropriate selection of IZ. These inputs act in the same manner as a virtual ground input of an operational amplifier and thus can serve as a summing node for any number of voltage and/or current signals. Outputs of components such as current output DACs, transconductance amplifiers and current conveyors can be directly connected to the inputs. Ideally, a multiplier should give zero output if either one of its multiplying inputs is zero. A nonzero output under these conditions is caused by a combination of input and output referred offsets. An output referred offset can be thought of as a fixed value added to the output and thus only affects D.C. accuracy. An input referred offset at a multiplying input allows signal to feedthrough from the other multiplying input to the output(s). The EL4083 is trimmed during testing at Elantec for X and Y input referred offset for IZ = 1.6 mA. The internal trim networks provide a current to each input which nulls the feedthrough caused by internal device mismatches. These current values are ratioed to the value of IZ so that the input referred nulls are largely maintained at different values of IZ. However, there will be some mistracking in the trim networks so that the input referred null point will deviate away from zero at values of IZ lower than 1.6mA. Figure 9 shows optional external input and output referred offset trim networks which can be used as needed to improve performance. As mentioned, the output referred offset only affects D.C. accuracy which may not be an issue in A.C. applications. In gain control applications one may only need to null feedthrough with respect to the gain control input. In gain control (VCA) applications the X input should be used as the control input and the signal applied to the Y input since it has slightly higher bandwidth and better linearity and distortion performance. Current Outputs (IXY, IXY), Feedthrough and Distortion Another unique feature of the EL4083 is the differential ground referenced current output structure. These outputs can drive 50 Ω terminated lines and reactive loads such as transformers, baluns, and LC tank and filter circuits directly (See EL2082 Data Sheet_Receiver IF Amplifier (Figure 19). The EL2082 also has a current output.). Unlike low impedance follower buffers, these outputs do not interact with the load to produce ringing or instability. If a high level low impedance output is required, the outputs can be recovered differentially and converted to a single ended output with a fast op amp such as the EL2075 (see Figure 19). The outputs can also drive current input devices such as CMF amps, current conveyors and its own inputs directly by simple connection. Figures 12 and 14 show the nulled gain and feedthrough characteristics of the IXY and IXY outputs which are virtually identical and differ only in phase. Figure 12 is with the A.C. signal applied to the X input with Y used as the gain control and in Figure 14 these signals are reversed. Note that in both cases the signal feedthrough rolls up and peaks near the cutoff frequency. This is quite typical of the performance of all previous four quadrant multipliers. Figures 13 and 15 show the corresponding gain/feedthrough characteristics for the differentially recovered output signal IXY-IXY. Note that in this case the peak feedthrough at high frequencies is lower by more than 40dB (See EL2082 Data Sheet - Receiver IF Amplifier [Figure 19]. The EL2082 also has a current output). General Operating Information Figures 16 and 17 show the total harmonic distortion for the single-ended and differential recovered outputs for a full scale A.C. input signal on one input and a full scale D.C. control signal on the other. Note that above about one megahertz to the cutoff frequency the THD of the differentially recovered signal is as much as 10dB lower than the single-ended signals. |
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