Quartz Tuning Fork Charge Amplifier HQA-15M-10T


  • High gain of 1 x 1013 V/C
  • Wide bandwidth from 250 Hz to 15 MHz
  • Low input noise of 40 zC/√Hz and 700 pV/√Hz
  • Excellent signal-to-noise ratio across the full bandwidth
  • Ideal for AC coupled charge sources such as pyro- and piezoelectric detectors, tuning fork quartz crystals and longitudinal resonators
Charge Gain 1 x 1013 V/C
Equivalent Current Gain1.6 x 106 V/A @ 1 MHz sinusoidal input signal
Lower Cut-Off Frequency250 Hz
Upper Cut-Off Frequency15 MHz
Input Charge Noise40 x 10-21 C/√Hz @ 1 MHz
Equivalent Input Current Noise250 fA/√Hz @ 1 MHz sinusoidal input signal
Input Voltage Noise700 pV/√Hz @ 1 MHz
Input Impedance1 GΩ || 10 nF
Effective AC Input Impedance20 Ω @ 1 MHz sinusoidal input signal
Output Performance10 V peak-peak @ 1 MΩ load
Power Requirements± 15 V, ± 35 mA typ.
Case94 x 51 x 27 mm (L x W x H), weight 200 g (0.44 lb.)

Output short-circuit protected. Power supply via 3-pin Lemo® socket. A mating connector is provided with the device. Optional power supply PS-15 available. For further information please view the datasheet or contact FEMTO.

Excellent signal to noise ratio

The HQA-15M-10T is designed for amplifying charge signals generated by tiny tuning forks. It is also best suited for receiving signals from piezoelectric detectors, such as used for the detection of ultrasonic vibrations. Using the charge amplifier HQA-15M-10T reduces noise typically by one order of magnitude compared to traditional current-to-voltage converter setups.   

The special operating mode of charge amplifiers

A charge amplifier is a current integrator. An output voltage is generated which is proportional to the charge accumulated at the amplifier input over a certain period of time. A charge amplifier often needs a reset mechanism to avoid overloading the integration stage. The HQA-15M-10T was developed for AC signal sources that do neither have nor generate a DC component on average over time. The charge of such sources is symmetrically alternating positive and negative. Since the resulting charge is zero, the HQA-15M-10T does not require a reset.

The difference between a current and a charge amplifier

The output signal of a current amplifier (synonymous with transimpedance amplifier) is directly proportional to the input current. The current is the derivative of the charge with respect to time. Therefore, the output signal of a current amplifier corresponds to the derivative of the output signal of an equivalent charge amplifier.

Charge measurements down to pico and femtocoulomb range

The HQA-15M-10T was developed for AC charge sources such as tuning fork crystals and longitudinal resonators. The amplifier is characterized by a very low-noise design and high gain in order to achieve excellent sensitivity for charge measurements down to the pico and femtocoulomb range. In contrast to some other amplifiers, the HQA-15M-10T does not require cooling, which results in a much more compact design and easier handling. The small housing enables use near the signal source and thus avoids signal interference from long cables. After all, the large bandwidth from 250 Hz to 15 MHz is ideal for versatile use with a large selection of suitable signal sources.


  • Pyro and piezoelectric detectors
  • Tuning fork quartz crystals
  • Longitudinal resonators
  • Atomic force microscopy (AFM)

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Power Supply