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Key Features:

  • Negative voltage line injector
  • Modulate a DC Power Source Voltage
  • Combines modulation signal with bus voltage
  • 10Hz-50MHz usable bandwidth
  • Low Impedance, Low Noise, and Low Voltage-Compliance
  • 3 Amps maximum current
  • -30VDC max input
  • Easily measure input filters and PSRR


What's included:

J2123A Line Injector
User manual
1 Year Warranty



The J2123A negative voltage line injector, like the J2120A positive voltage line injector, is used to superimpose an AC modulation signal on a DC source voltage for Power Supply Rejection Ratio (PSRR), Power Supply Modulation Ratio (PSMR), and Audio Amplifier Common-Mode Rejection Ratio (CMRR) testing. These applications require very low output noise, as well as a low output impedance over a wide bandwidth.


The Picotest J2123A, like the Picotest J2120A (for positive voltages), achieves these difficult requirements using a passive design to assure optimum performance.

The J2123A can be used in either time or frequency domain testing. Most often, the line injector allows the input DC supply voltage to be modulated by the network analyzer source signal, as in the case of a PSRR measurement. The line injector must be capable of a frequency range well below the AC line frequency and at least above the control loop bandwidth of the circuit being tested. A connection diagram using the OMICRON Lab Bode 100 is shown.


Note: The J2123A will be damaged if the input voltage is reversed. In a negative voltage system, the return jack (Black ground or 0 volts) should be more positive than the MINUS SUPPLY connection (Red).


The line injector is only capable of sourcing current, so that the output amplitude can be significantly impacted by the operating current and the total storage capacitance at the load. Graphs of the J2123A voltage output (relative to the input voltage) vs. the output provided are shown in the Detailed Specifications tab. The lower the (AC) impedance you want to drive, the higher the current and, therefore, the greater the voltage drop. Driving low impedance capacitive inputs may be challenging at higher frequency. It is recommended that you know and/or measure the AC impedance vs. frequency you need to drive.


To get a constant, known voltage at the DUT input, you can adjust the lab supply output voltage for each load current operating point. The J2123A also supports usage of a remote sense circuit connection with wide enough compliance to compensate for the J2123A voltage drop.


The line injector can also be used in conjunction with a current probe to measure the input impedance of a power supply. The input impedance of a switching power supply or regulator is negative, which creates a stability concern when combined with an EMI filter. As a result, the measurement is an important part of the design, analysis, and verification process. You can correct for the scaling by performing the THROUGH calibration with a 1 Ohm resistor.

Picotest J2123A Negative Voltage PSRR Injector

  • Maximum DC Input Voltage -30 VDC
    Maximum Continuous Current 3 A
    Maximum Voltage Drop 3 VDC
    3dB Frequency Response 20-20M Hz
    Useable Frequency Response 10-50M Hz
    Recommended Injection Signal -20 – 10 dBm
    Temperature Range 0-50 C
    Maximum Altitude 6000 Ft
    Absolute Maximum Voltage < -50V (DC + AC)


    Vdrop and Rout vs. Current

    The voltage drop and output resistance, as a function of output DC current is approximated by this set of equations:

    V(I) =2.312*I^(0.055)+I*0.09


    To avoid equipment damage and/or severe injuries or death ensure that the absolute maximum ratings are observed and not exceeded at all times. EMI Note: Exceeding 0dBm may cause the unit to exceed CE EMI limits.

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