Functional Overview

This chapter provides an overview of the VHFLI Lock-in Amplifier features. It covers the hardware and software features, the front and back panels, and the ordering guide.

Features

Lock-in Operating Modes

• Internal reference mode
• External reference mode
• Dual channel operation: two independent lock-in amplifiers in the same box
• Arbitrary frequency mode (with VHF-MD option): simultaneous measurement at up to 8 arbitrary frequencies and/or harmonics

Signal Inputs

• 2 low-noise voltage inputs with variable ranges from ±5 mV to ±2 V peak (10 MΩ input impedance)
• Frequency range: DC – 50 MHz (200 MHz with VHF-F200M option)
• Selectable AC/DC coupling for Voltage Inputs
• 2 low-noise current inputs with variable ranges from ±10 nA to ±10 mA

Signal Outputs

• 2 low-noise voltage outputs, DC - 50 MHz (200 MHz with the VHF-F200M option)
• Variable output range, from ±5 mV to ±5 V peak (into high-impedance load)

Demodulators & Reference

• Up to 8 dual-phase demodulators and 8 programmable numerical oscillators (with the VHF-MD option)
• Up to 2 external reference signals
• Individually programmable demodulator filters
• 128-bit internal processing
• 64-bit resolution demodulator sample
• 48-bit internal reference resolution

Auxiliary Input and Outputs

• 4 auxiliary outputs for user-defined signals, > 13 MHz bandwidth, 14 bit, with variable gain ranges, from ±100 mV to ±10 V
• 2 auxiliary inputs, ≥150 MHz bandwidth (-6 dB), with variable gain ranges from ±100 mV to ±10 V

High-speed Connectivity

• BNC connectors on front and SMA connectors on back panel
• USB-C high-speed host interface
• LAN/Ethernet 1 Gbit/s controller interface
• Up to 2 input and up to 2 output trigger signals
• DIO: 32-bit digital input-output port
• Clock input/output connectors (10/100 MHz)

Analysis and Automation Tools

• Numeric tool
• Plotter
• Oscilloscope
• Sweeper and Frequency response analyzer
• FFT spectrum analyzer
• Data Acquisition tool
• Timeline Module

Software Features

• LabOne® user interface with simultaneous multi-instrument control
• LabOne® user interface with simultaneous multi-instrument control
• Data server with multi-client support
• API for Python, MATLAB®, LabVIEW™, .NET, and C.

Front Panel Tour

The front panel BNC connectors and control LEDs are arranged as shown in Figure 1 and described in Table 1.

Figure 1: VHFLI Lock-in Amplifier front panel

Table 1: VHFLI Lock-in Amplifier front panel description

Position	Label / Name	Description
A	Signal Input I	single-ended current input
B	Signal Input –V Diff	voltage input
				single-ended mode: floating
				differential mode: negative voltage input
C	Signal Input +V	voltage input
				single-ended mode: single-ended voltage input
				differential mode: positive voltage input
D	Signal Output +V	voltage output
				single-ended mode: single-ended voltage output
				differential mode: positive voltage output
E	Signal Output –V Diff	voltage output
				single-ended mode: internally shorted to ground
				differential mode: negative voltage output
F	Aux Inputs	auxiliary inputs 1 and 2
G	Aux Outputs	auxiliary outputs 1 to 4
H	Trig Inputs	trigger inputs 1 and 2
I	Trig Outputs	trigger outputs 1 and 2
J	Signal Input I Over	Red LED: current input signal is saturating the A/D converter. Increase the current input range or attenuate the signal.
K	Signal Input V Over	Red LED: voltage input signal is saturating the A/D converter. Increase the voltage input range or attenuate the signal.
L	Signal Output ON	Blue LED: signal output is actively driven.
M	multicolor LEDs	off Instrument off or uninitialized blink all LEDs blink for 5 seconds → indicator used by the Identify Device functionality
		Busy	unused
		Ext. Clock	off 10/100 MHz External Clock Signal not present/detected blue 10/100 MHz External Clock Signal is present and locked on to yellow 10/100 MHz External Clock Signal present, but not locked on to red 10/100 MHz External Clock Signal present, but lock failed
		ZSync	unused
		Status	off Instrument off or uninitialized blue Instrument is initialized and has no warnings or errors yellow Instrument has warnings red Instrument has errors
N	Soft power button	Power button with incorporated status LED off Instrument off and disconnected from mains power blue flashing rapidly (>1/sec): Firmware is starting flashing slowly (<1/sec): Firmware ready, waiting for connection constant: Instrument ready and active connection over USB or Ethernet red breathing: Instrument off but connected to mains power → safe to power off using the rear panel switch, or restart using the soft power button flashing: Instrument booting up constant: Fatal error occurred

Back Panel Tour

The back panel is the main interface for power, control, service, and connectivity to other ZI instruments. Refer to Figure 2 and Table 2 for the detailed description of the items.

Figure 2: VHFLI Lock-in Amplifier back panel

Table 2: VHFLI Lock-in Amplifier back panel description

Position	Label / Name	Description
A	AC 100 - 240 V	Power inlet, fuse holder, and power switch
B	Earth ground	4 mm banana jack connector for earth ground, electrically connected to the chassis and the earth pin of the power inlet
C	MDS 1 & 2	SMA: bidirectional TTL ports for multi-device synchronization
D	Maintenance USB-C	USB-C port Attention: This port offers limited data throughput; the USB-C port (see position G) is recommended for normal operation
E	LAN 1GbE	1 Gbit LAN connector for instrument control and data acquisition
F	DIO 32bit	32-bit digital input/output (DIO) connector
G	USB-C	USB-C 3.0 port for instrument control and data acquisition
H	ZSync Primary	unused Attention: This is not an Ethernet plug, connection to an Ethernet network might damage the instrument
I	External Clk In and Out	External clock (10 MHz/100 MHz) Input and Output for synchronization with other instruments

Ordering Guide

Table 3 provides an overview of the available VHFLI products. Upgradeable features are options that can be purchased anytime without the need to send the instrument back to Zurich Instruments.

Table 3: VHFLI product codes for ordering

Product code	Product name	Description	Field upgrade possible
VHFLI	VHFLI Lock-in Amplifier	base lock-in amplifier	-
VHF-F200M	VHF-F200M 200 MHz Frequency extension	option	yes
VHF-MD	VHF-MD Multi-demodulator	option	yes
VHF-MOD	VHF-MOD AM/FM Modulation	option	yes1
VHF-PID	VHF-PID Quad PID/PLL Controller	option	yes
VHF-AWG	VHF-AWG Arbitrary Waveform Generator	option	yes
VHF-BOX	VHF-BOX Boxcar Averager Option	option	yes
VHFLI-OB50	VHFLI 50 MHz Option Bundle	bundle	no
VHFLI-FOB	VHFLI Full-Option Bundle	bundle	no

¹ Requires VHF-MD Multi-demodulator option