Guzik active high-impedance injector is designed for the measurements of frequency response and the calibration of the low-impedance current-sensitive head amplifiers. The injector also provides the ability to evaluate the performance of the head-amplifier heater driver. A current probe can be connected to the injector, in order to measure write current of the head amplifier.

The injector converts the single-ended signal from a network analyzer or a signal generator to a differential signal and attenuates the level of the signal, so it can be connected to the input of a head amplifier. Due to the high output impedance (1280 Ohm), the injector acts as a current source.

The injector has the bandwidth from DC to 3 GHz and provides a differential output signal with the high symmetry of frequency response and group delay. The bandwidth starts from DC to measure the frequency response of the read-back amplifiers for perpendicular recording. The injector also has a bypass biasing circuitry to work with the majority of the commercial amplifiers.

The external devices, such as an oscilloscope or the load simulating the heating element of a head, can be connected to the three-pin heater-driver connector (scope points) on the active injector. This connector provides the positive output F+, the negative output F–, and the ground output GND.

Head Amplifier Active Injector Specifications:

Frequency Response

Bandwidth: DC to 3 GHz
Flatness: ±0.2 dB, 100 kHz to 2 GHz, ±1 dB, DC to 3 GHz (50 Ohm load)
Amplitude Difference Between Positive and Negative Outputs:
less than 0.5 dB

Group Delay

Flatness: better then 100 psec to 3 GHz
Difference Between Positive and Negative Outputs: less than 25 psec

Output Impedance

Nominal: 1280 Ohm differential

Attenuation

Single Ended Input to Differential Output: 38 dB typical with 50 Ohm termination (see Figure 1 for more details)

Power Supply

±5 V, 120 mA from the power filter of
RWA Analog Box

Items available: CCW Cartridge with Active Injector Board (Guzik P/N S80-703408), CW Cartridge with Active Injector Board (Guzik P/N S80-703409), and Power Filter Cable (Guzik P/N 30-461017). Separate Injector Boards CCW (Guzik P/N 23-327930) and CW (Guzik P/N 23-327920) can be ordered as spare parts.

active injector attenuation

Figure 1: Active Injector Attenuation

Frequency Response and Group Delay

frequency response and group delay

Figure 3: Group Delay of Head Amplifier Active Injector

Connecting Current Probe

To measure the write current of a magnetic head, a probe can be connected directly to the active high-impedance injector. Connecting the current probe is simple: remove the zero-Ohm resistor and solder the wire loop of the current probe to Via 1 and Via 2 reserved for the loop connection (see Figure 4). The recommended probe is Tektronix CT-6.

current probe connection diagram

Active Head-Impedance Injector for Head Amplifier of V2002 Spinstand – Discontinued