Mirrored enhanced Howland current source with feedback control

Abstract

An impedance spectrum is calculated by the ratio between an injecting current and a resulting measured voltage, which allows the extraction of electrical properties from the material under study. The current source is considered an essential block to deliver a controlled current to a wide range of working loads and large bandwidth. To comply with such requirements, the current source output impedance must be much higher than the load impedance at each discrete frequency within the range. However, stray capacitance from cables and circuitry reduce the output impedance, especially at higher frequencies. We proposed a modified mirrored enhanced Howland current source (MEHCS) by using the feedback technique for a wide frequency range applications on electrical bioimpedance. We implemented four MEHCS circuits [with/without multiplexer (MUX) and with/without feedback], and then the output current and impedance were measured up to 20 MHz. The proposed current source showed an improvement in the frequency response at lower and higher frequencies when compared to the standard circuit. The measured output impedance was 10 times higher in the proposed circuit than in the standard MEHCS. The use of a feedback also increased the bandwidth in almost one decade in low and high frequencies when loaded with a resistor of about 1 kΩ.

Temporal interference current stimulation in peripheral nerves

“…A full circuit schematic is shown in the supplement. We utilized a mirrored Howland current source as proposed by 29,30 for each stimulator channel. We additionally included a DC blocking capacitor at the output, to prevent DC leakage during stimulation, which can skew recruitment curves 31 .…”

A Multi-Frequency Focused Impedance Measurement System Based on Analogue Synchronous Peak Detection

“…Wilson et al, 2001). A recent development of the former approach has shown that using the measured current to control the output current from the current source gives a current source with a high output impedance when multiplexers are used (Sirtoli et al, 2019). All these approaches have substantial cost and complexity implications but should be considered as part of future developments.…”

Stability analysis and design of floating load voltage‐controlled current sources

“…The analysis of the literature and technical documentation showed the existence of two basic types of circuit configurations that work with floating or grounded load. In previous works, 5–14 different circuits of voltage‐to‐current converters with grounded load are presented, in which various useful structural modifications and frequency compensations with external passive components are proposed for improving the stability in a given frequency range, as well as increasing the value of the output resistance. Moreover, the majority of the electronic circuits 3–6,8–12,14 are based on the Improved Howland Current Pump, which uses one op‐amp and five (or six) resistors.…”

“…In previous works, 5–14 different circuits of voltage‐to‐current converters with grounded load are presented, in which various useful structural modifications and frequency compensations with external passive components are proposed for improving the stability in a given frequency range, as well as increasing the value of the output resistance. Moreover, the majority of the electronic circuits 3–6,8–12,14 are based on the Improved Howland Current Pump, which uses one op‐amp and five (or six) resistors. For the Improved Howland Current Pump, with an accurate selection of the ratios of the resistors and proper selection of the op‐amp, the independence of the output current from the voltage drop over the load can be achieved, as well as the bandwidth can up to about 100 kHz 6,10,12–14 and in some cases up to 1 MHz 5,8,9,11 .…”

“…Moreover, the majority of the electronic circuits 3–6,8–12,14 are based on the Improved Howland Current Pump, which uses one op‐amp and five (or six) resistors. For the Improved Howland Current Pump, with an accurate selection of the ratios of the resistors and proper selection of the op‐amp, the independence of the output current from the voltage drop over the load can be achieved, as well as the bandwidth can up to about 100 kHz 6,10,12–14 and in some cases up to 1 MHz 5,8,9,11 . For the circuits given in previous studies, 3,4,15–17 topological structures are used in which the load is connected between two terminals that are not directly connected to the analog ground.…”