HLVA Logarithmic Voltage Amplifier

Use 60 dB as the normal design range when quantitative amplitude accuracy is required, while 80 dB is the maximum range intended for signal detection. The logarithmic transfer uses a scaling of 12.5 mV/dB, equivalent to 250 mV per decade into a 50 Ω load, so large input changes are compressed into smaller output changes. Linearity is specified at ±1 dB for pulses with a minimum width of 20 ns. In practice, designs that compare pulse amplitudes should remain within the 60 dB region, while the additional range can be used for event detection or thresholding.

Select ±20 µV to ±200 mV for lower-level signals and ±200 µV to ±2 V for higher input amplitudes. The range can be changed locally or remotely; with the local switch set to ±2 V, Pin 10 selects ±2 V at a low logic level and ±200 mV at a high level. The absolute maximum input is ±3 V on the ±2 V setting, while the ±200 mV setting permits −3 V to +300 mV. These limits are protection ratings rather than measurement ranges, so normal peaks should remain inside the selected operating span. Range selection lets an automated system trade lower-level sensitivity against a higher allowable signal amplitude.

The amplifier may respond to shorter events, but quantitative amplitude performance is defined only for pulse widths of 20 ns or more. Its rise and fall time is 5 ns for a 40 dB step, and the signal path covers DC to 100 MHz, which supports fast transient detection. However, the ±1 dB linearity specification is tied to the 20 ns minimum pulse width and should not be applied to narrower pulses without validation. Maintain a 50 Ω source, cable path and receiving termination because the scaling and output range are specified for a 50 Ω system. For sub-20 ns measurements, verify the complete signal chain with representative pulses before establishing amplitude limits or detection thresholds.

Manual input-offset trimming, external offset control and remote baseline correction address different integration requirements. The input offset can be adjusted over ±2.5 mV by trimmer or through an external ±10 V control signal applied to a 100 kΩ input; a separate output-offset trimmer provides ±500 mV adjustment. The sample-and-hold baseline function requires a 30 µs acquisition pulse, has a typical hold droop of 1 µV/s at 25 °C and uses a 1.5 kHz loop cut-off. Manual trimming suits fixed bench setups, whereas external control supports system-level analogue correction. Remote automatic nulling is useful between measurement events when the control pulse can be applied during a known baseline interval.

Remote control is provided through a female 25-pin Sub-D connector, with opto-isolated digital functions for range selection and baseline correction. Digital low is −0.8 to +0.8 V and digital high is +3 to +12 V, making the inputs compatible with TTL and CMOS logic. At +5 V, the range-control input draws 1.5 mA and the baseline-control input draws 7 mA; Pin 9 is the digital ground reference. Pin 10 selects the input range, while Pin 11 holds the previous baseline at low level and commands nulling at high level. The local range switch and remote command are logically combined, so the local switch must remain at ±2 V when software or external logic is intended to control the range.

Use a 50 Ω signal path with BNC connections at both the input and output. The specified 12.5 mV/dB scaling and typical +50 to +1075 mV output range apply with a 50 Ω load, so the receiving instrument should have a 50 Ω input or use an appropriate external termination. Shielded 50 Ω RF cable helps maintain impedance continuity and reduce electromagnetic pickup. Cable length and connector transitions should be considered when preserving the 5 ns pulse response, particularly in time-resolved measurements. Before calibration, confirm the actual termination at the oscilloscope, digitiser or data-acquisition input rather than relying only on the cable’s nominal impedance.

The unit requires a regulated ±15 V supply and typically draws +90 mA from the positive rail and −120 mA from the negative rail. Power enters through a three-pin LEMO Series 1S socket; the absolute maximum supply voltage is ±20 V and must not be treated as a normal operating condition. The control connector also provides stabilised ±12 V outputs rated at up to 100 mA and a +5 V output rated at up to 50 mA. Operation is specified from 0 to +60 °C, with storage from −40 to +100 °C, and the nickel-plated AlMg4.5Mn enclosure weighs 320 g. Supply sizing should include any loads connected to the auxiliary outputs and maintain stable rails during fast pulse activity.