This is work in progress project, updates will be posted frequently.
“If you have to ask the price, you can’t afford it”
Layout of the 6-layer custom ceramic PCB:
Cross-section of the PCB
Module assembled with some additional shielding
Air baffles to reduce thermal gradients around LTZ1000A chips.
Module installed in Keysight 3458A DMM, replacing onboard A9 LTZ1000A-module
Preliminary 0.1 – 10 Hz noise test results, room temperature.
QVR Unit #1 was mostly kept unpowered to evaluate deviation and instability of the quad LTZ1000A-based reference module. Measurements were handled at two different locations with international shipping of the unit with regular postal service (USPS at US end, EMS at NMI location).
Calibration reference value T23°C = 9.990901 VDC ±0.8 ppm , 10.SEP.2019
Calibration result from NMI (Calibrated 3458A readout)
Calibration reference value T23°C = 9.990904 VDC ±0.6 ppm , 17.JAN.2021
Then standard was returned and tested again, powered from Fluke 792X battery power pack.
Calibration reference value T17°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Calibration reference value T23°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Calibration reference value T30°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Calibration reference value T45°C = 9.9909107 VDC ±0.6 ppm , 1.APR.2021
Second prototype batch with ADR1000AHZ superzeners
SN0004 – Dual ADR-chip module with 10V output
|Zener||C: ADR1000AHZ, A: ADR1000AHZ||unaged new chips, 6mm mount gap to PCB, 13mm total top Z height|
|Temp setpoint||C: 11500:1000 Ω VHD200, A: 13000:1000 Ω VHD200||C:new chip, A: network S/N 8|
|IZ setpoint||Both 80 Ω VHP202ZT||new chips, random run, not selected|
|BiasR||4 × 62 kΩ MELF0204 5 ppm/K|
|Opamp||OPA2140 for zener cells, ADA4522-2 for output stage|
|Output scale||RDIV VHD200 10000:5105 Ω||R11:R9 position|
|TC trim oven||C: TBD, A: TBD|
|Capacitors||C: 100nF C0G, A: 100nF Film|
|Power||Onboard LT3045||+12VDC output voltage point|
Noise performance of SN0004 unit
Here are noise measurement results with battery-operated QVR module and battery operated 80 dB 0.1-10Hz AC coupled LNA.
C Cell : RAW output noise (+6.62 VDC from Zener core) measurement in 0.1 – 10 Hz bandwidth :
Average value is 377 nV peak to peak, which is good for a single ADR zener. Measurement standard deviation is 34 nVptp.
A Cell : RAW output noise (+6.62 VDC from Zener core) measurement in 0.1 – 10 Hz bandwidth :
This cell operates at higher oven temperature around +75 °C.
Average value is 395 nV peak to peak, which is good for a single ADR zener. Measurement standard deviation is 41 nVptp.
Now A+C combined cells with 250||250 foil resistors. This is combined RAW output noise (+6.62 VDC from two zener cores) measurement in 0.1 – 10 Hz bandwidth.
Average value is 281 nV peak to peak, which is promising result with just two ADR zeners. Measurement standard deviation is 24 nVptp. This is pretty close to quad LTZ1000A-based QVR results, which was ~248 nV peak to peak with same measurement setup.
Noise floor of this noise measurement setup is around 100 nV peak to peak.
Modified: Jan. 11, 2023, 8:39 a.m.