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PSP FIELDS Digital Fields Board (DFB), Differential Voltage data. 
The DFB is the low frequency (< 75 kHz) component of the FIELDS experiment on the Parker Solar Probe spacecraft [1]. For a full description of the FIELDS experiment, see [2]. For a description of the DFB, see [3].
DFB continuous waveform data consist of time-series data from various FIELDS sensors. These data have been filtered by both analog and digital filters [3]. 
The Level 2 data products contained in this data file have been calibrated for (i) DFB in-band gain, (ii) DFB analog filter gain/phase response, (iii) DFB digital filter phase response, and (iv) the search coil preamplifier gain/phase response (when applicable). Calibrations for the FIELDS digital filter gain response have not been implemented, but the required convolution kernel is provided in this file.  It was decided not to apply the FIELDS digital filter gain response to the L2 data because this can introduce non-physical power at high frequencies when the non-corrected signal is dominated by noise. This effect should be examined carefully when determining spectral slopes and features at the highest frequencies. Calibrations for the FIELDS voltage sensor preamplifiers have not been implemented, as the preamplifier response is flat and equal to 1 through the DFB frequency range.  Corrections for plasma sheath impedance gain and antenna effective length have not been applied to the voltage sensor data (these corrections will be applied in Level 3 DFB data), therefore units for all voltage sensor quantities are Volts.  Units for all magnetic field quantities are nT.
The Level 2 data products contained in this data file are in spacecraft coordinates (e.g. x,y,z) and in sensor coordinates (e.g. dV12, dV34 for voltage measurements, and u,v,w for the search coil magnetometer). 
Time resolution for the DFB continuous waveform data can vary by multiples of 2^N.  During encounter (when PSP is within 0.25 AU of the Sun), cadence for the DFB continuous waveform data is typically 256 samples/NYsecond [2].  
References: 
1. Fox, N.J., Velli, M.C., Bale, S.D. et al. Space Sci Rev (2016) 204: 7. https://doi.org/10.1007/s1121401502116 
2. Bale, S.D., Goetz, K., Harvey, P.R. et al. Space Sci Rev (2016) 204: 49. https://doi.org/10.1007/s1121401602445 
3. Malaspina, D.M., Ergun, R.E., Bolton, M. et al. (2016) JGR Space Physics, 121, 5088-5096. https://doi.org/10.1002/2016JA022344

Kernel (real part) needed to correct for digital filter response

Kernel (imaginary part) needed to correct for digital filter response

Noise floor for high gain differential voltages in sensor coordinates

Noise floor for low gain differential voltages in sensor coordinates

Matrix for converting differential voltage data in sensor coordinates [dV12,dV34] to spacecraft coordinates [dX,dY]. The transformation is not a simple rotation matrix because the dipole antennas on PSP are non-orthogonal. The matrix is defined as the inverse of [[cos(55),sin(55)],[-cos(40),sin(40)]]. Details on the PSP antenna orientations can be found in the PSP/FIELDS frame kernel.

FIELDS quality flags. This is a bitwise variable, meaning that multiple flags can be set for a single time, by adding flag values. Current flagged values are: 1: FIELDS antenna bias sweep, 2: PSP thruster firing, 4: SCM Calibration, 8: PSP rotations for MAG calibration (MAG rolls), 16: FIELDS MAG calibration sequence, 32: SWEAP SPC in electron mode, 64: PSP Solar limb sensor (SLS) test. 128: PSP spacecraft is off umbra pointing. 256: High frequency noise affecting RFS and TDS receivers. 512: Antennas driven towards the FIELDS power supply rails. A value of zero corresponds to no set flags. Not all flags are relevant to all FIELDS data products, refer to notes in the CDF metadata and on the FIELDS SOC website for information on how the various flags impact FIELDS data. For more information on the quality flags describing high frequency noise and antennas driven to the rails, see release notes for PSP/FIELDS releases 8 and 9. Additional flagged items may be added in the future.