xDevs.com QVR - Ultra-low noise DC Voltage reference

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

First module:

Second module:

Performance

Preliminary 0.1 – 10 Hz noise test results, room temperature.

Long-term stability.

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

1st temperature sweep prior to shipping for NMI
2nd temperature sweep prior to shipping for NMI

Calibration result from NMI (Calibrated 3458A readout)

Calibration transfers on DC Zener bank array at NMI

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

Datalog with triple 3458A, in thermal chamber

Second prototype batch with ADR1000AHZ superzeners

SN0004 – Dual ADR-chip module with 10V output

Parameter Property Note
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
Output cap None
Z6 network TBD
EEPROM None

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.

Author: Illya Tsemenko
Created: Sept. 20, 2019, 2:12 p.m.
Modified: Jan. 11, 2023, 8:39 a.m.

References